diff --git a/examples/okex-book/main.go b/examples/okex-book/main.go
index 77218d81c..e6e7341cc 100644
--- a/examples/okex-book/main.go
+++ b/examples/okex-book/main.go
@@ -44,10 +44,13 @@ var rootCmd = &cobra.Command{
 			return errors.New("empty key, secret or passphrase")
 		}
 
-		client := okexapi.NewClient()
+		client, err := okexapi.NewClient()
+		if err != nil {
+			return errors.New("init client error: please check url")
+		}
 		client.Auth(key, secret, passphrase)
 
-		instruments, err := client.PublicDataService.NewGetInstrumentsRequest().
+		instruments, err := client.NewGetInstrumentsRequest().
 			InstrumentType("SPOT").Do(ctx)
 		if err != nil {
 			return err
@@ -55,14 +58,14 @@ var rootCmd = &cobra.Command{
 
 		log.Infof("instruments: %+v", instruments)
 
-		fundingRate, err := client.PublicDataService.NewGetFundingRate().InstrumentID("BTC-USDT-SWAP").Do(ctx)
+		fundingRate, err := client.NewGetFundingRate().InstrumentID("BTC-USDT-SWAP").Do(ctx)
 		if err != nil {
 			return err
 		}
 		log.Infof("funding rate: %+v", fundingRate)
 
 		log.Infof("ACCOUNT BALANCES:")
-		account, err := client.AccountBalances()
+		account, err := client.AccountBalances(ctx)
 		if err != nil {
 			return err
 		}
@@ -70,7 +73,7 @@ var rootCmd = &cobra.Command{
 		log.Infof("%+v", account)
 
 		log.Infof("ASSET BALANCES:")
-		assetBalances, err := client.AssetBalances()
+		assetBalances, err := client.AssetBalances(ctx)
 		if err != nil {
 			return err
 		}
@@ -80,7 +83,7 @@ var rootCmd = &cobra.Command{
 		}
 
 		log.Infof("ASSET CURRENCIES:")
-		currencies, err := client.AssetCurrencies()
+		currencies, err := client.AssetCurrencies(ctx)
 		if err != nil {
 			return err
 		}
@@ -90,7 +93,7 @@ var rootCmd = &cobra.Command{
 		}
 
 		log.Infof("MARKET TICKERS:")
-		tickers, err := client.MarketTickers(okexapi.InstrumentTypeSpot)
+		tickers, err := client.MarketTickers(ctx, okexapi.InstrumentTypeSpot)
 		if err != nil {
 			return err
 		}
@@ -99,7 +102,7 @@ var rootCmd = &cobra.Command{
 			log.Infof("%T%+v", ticker, ticker)
 		}
 
-		ticker, err := client.MarketTicker("ETH-USDT")
+		ticker, err := client.MarketTicker(ctx, "ETH-USDT")
 		if err != nil {
 			return err
 		}
@@ -107,7 +110,7 @@ var rootCmd = &cobra.Command{
 		log.Infof("%T%+v", ticker, ticker)
 
 		log.Infof("PLACING ORDER:")
-		placeResponse, err := client.TradeService.NewPlaceOrderRequest().
+		placeResponse, err := client.NewPlaceOrderRequest().
 			InstrumentID("LTC-USDT").
 			OrderType(okexapi.OrderTypeLimit).
 			Side(okexapi.SideTypeBuy).
@@ -122,7 +125,7 @@ var rootCmd = &cobra.Command{
 		time.Sleep(time.Second)
 
 		log.Infof("getting order detail...")
-		orderDetail, err := client.TradeService.NewGetOrderDetailsRequest().
+		orderDetail, err := client.NewGetOrderDetailsRequest().
 			InstrumentID("LTC-USDT").
 			OrderID(placeResponse.OrderID).
 			Do(ctx)
@@ -132,7 +135,7 @@ var rootCmd = &cobra.Command{
 
 		log.Infof("order detail: %+v", orderDetail)
 
-		cancelResponse, err := client.TradeService.NewCancelOrderRequest().
+		cancelResponse, err := client.NewCancelOrderRequest().
 			InstrumentID("LTC-USDT").
 			OrderID(placeResponse.OrderID).
 			Do(ctx)
@@ -144,15 +147,15 @@ var rootCmd = &cobra.Command{
 		time.Sleep(time.Second)
 
 		log.Infof("BATCH PLACE ORDER:")
-		batchPlaceReq := client.TradeService.NewBatchPlaceOrderRequest()
-		batchPlaceReq.Add(client.TradeService.NewPlaceOrderRequest().
+		batchPlaceReq := client.NewBatchPlaceOrderRequest()
+		batchPlaceReq.Add(client.NewPlaceOrderRequest().
 			InstrumentID("LTC-USDT").
 			OrderType(okexapi.OrderTypeLimit).
 			Side(okexapi.SideTypeBuy).
 			Price("50.0").
 			Quantity("0.5"))
 
-		batchPlaceReq.Add(client.TradeService.NewPlaceOrderRequest().
+		batchPlaceReq.Add(client.NewPlaceOrderRequest().
 			InstrumentID("LTC-USDT").
 			OrderType(okexapi.OrderTypeLimit).
 			Side(okexapi.SideTypeBuy).
@@ -168,7 +171,7 @@ var rootCmd = &cobra.Command{
 		time.Sleep(time.Second)
 
 		log.Infof("getting pending orders...")
-		pendingOrders, err := client.TradeService.NewGetPendingOrderRequest().Do(ctx)
+		pendingOrders, err := client.NewGetPendingOrderRequest().Do(ctx)
 		if err != nil {
 			return err
 		}
@@ -176,9 +179,9 @@ var rootCmd = &cobra.Command{
 			log.Infof("pending order: %+v", pendingOrder)
 		}
 
-		cancelReq := client.TradeService.NewBatchCancelOrderRequest()
+		cancelReq := client.NewBatchCancelOrderRequest()
 		for _, resp := range batchPlaceResponse {
-			cancelReq.Add(client.TradeService.NewCancelOrderRequest().
+			cancelReq.Add(client.NewCancelOrderRequest().
 				InstrumentID("LTC-USDT").
 				OrderID(resp.OrderID))
 		}
diff --git a/pkg/exchange/factory.go b/pkg/exchange/factory.go
index 00d6db7c9..c7f3371ca 100644
--- a/pkg/exchange/factory.go
+++ b/pkg/exchange/factory.go
@@ -37,7 +37,7 @@ func New(n types.ExchangeName, key, secret, passphrase string) (types.ExchangeMi
 		return max.New(key, secret), nil
 
 	case types.ExchangeOKEx:
-		return okex.New(key, secret, passphrase), nil
+		return okex.New(key, secret, passphrase)
 
 	case types.ExchangeKucoin:
 		return kucoin.New(key, secret, passphrase), nil
diff --git a/pkg/exchange/okex/exchange.go b/pkg/exchange/okex/exchange.go
index 700b95837..92e322116 100644
--- a/pkg/exchange/okex/exchange.go
+++ b/pkg/exchange/okex/exchange.go
@@ -34,8 +34,11 @@ type Exchange struct {
 	client *okexapi.RestClient
 }
 
-func New(key, secret, passphrase string) *Exchange {
-	client := okexapi.NewClient()
+func New(key, secret, passphrase string) (*Exchange, error) {
+	client, err := okexapi.NewClient()
+	if err != nil {
+		return nil, err
+	}
 
 	if len(key) > 0 && len(secret) > 0 {
 		client.Auth(key, secret, passphrase)
@@ -46,7 +49,7 @@ func New(key, secret, passphrase string) *Exchange {
 		secret:     secret,
 		passphrase: passphrase,
 		client:     client,
-	}
+	}, nil
 }
 
 func (e *Exchange) Name() types.ExchangeName {
@@ -54,7 +57,7 @@ func (e *Exchange) Name() types.ExchangeName {
 }
 
 func (e *Exchange) QueryMarkets(ctx context.Context) (types.MarketMap, error) {
-	instruments, err := e.client.PublicDataService.NewGetInstrumentsRequest().
+	instruments, err := e.client.NewGetInstrumentsRequest().
 		InstrumentType(okexapi.InstrumentTypeSpot).
 		Do(ctx)
 
@@ -98,7 +101,7 @@ func (e *Exchange) QueryMarkets(ctx context.Context) (types.MarketMap, error) {
 func (e *Exchange) QueryTicker(ctx context.Context, symbol string) (*types.Ticker, error) {
 	symbol = toLocalSymbol(symbol)
 
-	marketTicker, err := e.client.MarketTicker(symbol)
+	marketTicker, err := e.client.MarketTicker(ctx, symbol)
 	if err != nil {
 		return nil, err
 	}
@@ -107,7 +110,7 @@ func (e *Exchange) QueryTicker(ctx context.Context, symbol string) (*types.Ticke
 }
 
 func (e *Exchange) QueryTickers(ctx context.Context, symbols ...string) (map[string]types.Ticker, error) {
-	marketTickers, err := e.client.MarketTickers(okexapi.InstrumentTypeSpot)
+	marketTickers, err := e.client.MarketTickers(ctx, okexapi.InstrumentTypeSpot)
 	if err != nil {
 		return nil, err
 	}
@@ -138,7 +141,7 @@ func (e *Exchange) PlatformFeeCurrency() string {
 }
 
 func (e *Exchange) QueryAccount(ctx context.Context) (*types.Account, error) {
-	accountBalance, err := e.client.AccountBalances()
+	accountBalance, err := e.client.AccountBalances(ctx)
 	if err != nil {
 		return nil, err
 	}
@@ -153,7 +156,7 @@ func (e *Exchange) QueryAccount(ctx context.Context) (*types.Account, error) {
 }
 
 func (e *Exchange) QueryAccountBalances(ctx context.Context) (types.BalanceMap, error) {
-	accountBalances, err := e.client.AccountBalances()
+	accountBalances, err := e.client.AccountBalances(ctx)
 	if err != nil {
 		return nil, err
 	}
@@ -163,7 +166,7 @@ func (e *Exchange) QueryAccountBalances(ctx context.Context) (types.BalanceMap,
 }
 
 func (e *Exchange) SubmitOrder(ctx context.Context, order types.SubmitOrder) (*types.Order, error) {
-	orderReq := e.client.TradeService.NewPlaceOrderRequest()
+	orderReq := e.client.NewPlaceOrderRequest()
 
 	orderType, err := toLocalOrderType(order.Type)
 	if err != nil {
@@ -257,7 +260,7 @@ func (e *Exchange) SubmitOrder(ctx context.Context, order types.SubmitOrder) (*t
 
 func (e *Exchange) QueryOpenOrders(ctx context.Context, symbol string) (orders []types.Order, err error) {
 	instrumentID := toLocalSymbol(symbol)
-	req := e.client.TradeService.NewGetPendingOrderRequest().InstrumentType(okexapi.InstrumentTypeSpot).InstrumentID(instrumentID)
+	req := e.client.NewGetPendingOrderRequest().InstrumentType(okexapi.InstrumentTypeSpot).InstrumentID(instrumentID)
 	orderDetails, err := req.Do(ctx)
 	if err != nil {
 		return orders, err
@@ -278,7 +281,7 @@ func (e *Exchange) CancelOrders(ctx context.Context, orders ...types.Order) erro
 			return ErrSymbolRequired
 		}
 
-		req := e.client.TradeService.NewCancelOrderRequest()
+		req := e.client.NewCancelOrderRequest()
 		req.InstrumentID(toLocalSymbol(order.Symbol))
 		req.OrderID(strconv.FormatUint(order.OrderID, 10))
 		if len(order.ClientOrderID) > 0 {
@@ -287,7 +290,7 @@ func (e *Exchange) CancelOrders(ctx context.Context, orders ...types.Order) erro
 		reqs = append(reqs, req)
 	}
 
-	batchReq := e.client.TradeService.NewBatchCancelOrderRequest()
+	batchReq := e.client.NewBatchCancelOrderRequest()
 	batchReq.Add(reqs...)
 	_, err := batchReq.Do(ctx)
 	return err
@@ -304,7 +307,7 @@ func (e *Exchange) QueryKLines(ctx context.Context, symbol string, interval type
 
 	intervalParam := toLocalInterval(interval.String())
 
-	req := e.client.MarketDataService.NewCandlesticksRequest(toLocalSymbol(symbol))
+	req := e.client.NewCandlesticksRequest(toLocalSymbol(symbol))
 	req.Bar(intervalParam)
 
 	if options.StartTime != nil {
@@ -349,7 +352,7 @@ func (e *Exchange) QueryOrder(ctx context.Context, q types.OrderQuery) (*types.O
 	if len(q.OrderID) == 0 && len(q.ClientOrderID) == 0 {
 		return nil, errors.New("okex.QueryOrder: OrderId or ClientOrderId is required parameter")
 	}
-	req := e.client.TradeService.NewGetOrderDetailsRequest()
+	req := e.client.NewGetOrderDetailsRequest()
 	req.InstrumentID(q.Symbol).
 		OrderID(q.OrderID).
 		ClientOrderID(q.ClientOrderID)
diff --git a/pkg/exchange/okex/okexapi/client.go b/pkg/exchange/okex/okexapi/client.go
index ccb81f70a..5d0533051 100644
--- a/pkg/exchange/okex/okexapi/client.go
+++ b/pkg/exchange/okex/okexapi/client.go
@@ -2,6 +2,7 @@ package okexapi
 
 import (
 	"bytes"
+	"context"
 	"crypto/hmac"
 	"crypto/sha256"
 	"encoding/base64"
@@ -14,7 +15,7 @@ import (
 
 	"github.com/c9s/bbgo/pkg/fixedpoint"
 	"github.com/c9s/bbgo/pkg/types"
-	"github.com/c9s/bbgo/pkg/util"
+	"github.com/c9s/requestgen"
 	"github.com/pkg/errors"
 )
 
@@ -60,34 +61,26 @@ const (
 )
 
 type RestClient struct {
-	BaseURL *url.URL
-
-	client *http.Client
+	requestgen.BaseAPIClient
 
 	Key, Secret, Passphrase string
-
-	TradeService      *TradeService
-	PublicDataService *PublicDataService
-	MarketDataService *MarketDataService
 }
 
-func NewClient() *RestClient {
+func NewClient() (*RestClient, error) {
 	u, err := url.Parse(RestBaseURL)
 	if err != nil {
-		panic(err)
+		return nil, err
 	}
 
 	client := &RestClient{
-		BaseURL: u,
-		client: &http.Client{
-			Timeout: defaultHTTPTimeout,
+		BaseAPIClient: requestgen.BaseAPIClient{
+			BaseURL: u,
+			HttpClient: &http.Client{
+				Timeout: defaultHTTPTimeout,
+			},
 		},
 	}
-
-	client.TradeService = &TradeService{client: client}
-	client.PublicDataService = &PublicDataService{client: client}
-	client.MarketDataService = &MarketDataService{client: client}
-	return client
+	return client, nil
 }
 
 func (c *RestClient) Auth(key, secret, passphrase string) {
@@ -97,44 +90,8 @@ func (c *RestClient) Auth(key, secret, passphrase string) {
 	c.Passphrase = passphrase
 }
 
-// NewRequest create new API request. Relative url can be provided in refURL.
-func (c *RestClient) newRequest(method, refURL string, params url.Values, body []byte) (*http.Request, error) {
-	rel, err := url.Parse(refURL)
-	if err != nil {
-		return nil, err
-	}
-
-	if params != nil {
-		rel.RawQuery = params.Encode()
-	}
-
-	pathURL := c.BaseURL.ResolveReference(rel)
-	return http.NewRequest(method, pathURL.String(), bytes.NewReader(body))
-}
-
-// sendRequest sends the request to the API server and handle the response
-func (c *RestClient) sendRequest(req *http.Request) (*util.Response, error) {
-	resp, err := c.client.Do(req)
-	if err != nil {
-		return nil, err
-	}
-
-	// newResponse reads the response body and return a new Response object
-	response, err := util.NewResponse(resp)
-	if err != nil {
-		return response, err
-	}
-
-	// Check error, if there is an error, return the ErrorResponse struct type
-	if response.IsError() {
-		return response, errors.New(string(response.Body))
-	}
-
-	return response, nil
-}
-
-// newAuthenticatedRequest creates new http request for authenticated routes.
-func (c *RestClient) newAuthenticatedRequest(method, refURL string, params url.Values, payload interface{}) (*http.Request, error) {
+// NewAuthenticatedRequest creates new http request for authenticated routes.
+func (c *RestClient) NewAuthenticatedRequest(ctx context.Context, method, refURL string, params url.Values, payload interface{}) (*http.Request, error) {
 	if len(c.Key) == 0 {
 		return nil, errors.New("empty api key")
 	}
@@ -215,13 +172,13 @@ type Account struct {
 	Details          []BalanceDetail  `json:"details"`
 }
 
-func (c *RestClient) AccountBalances() (*Account, error) {
-	req, err := c.newAuthenticatedRequest("GET", "/api/v5/account/balance", nil, nil)
+func (c *RestClient) AccountBalances(ctx context.Context) (*Account, error) {
+	req, err := c.NewAuthenticatedRequest(ctx, "GET", "/api/v5/account/balance", nil, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := c.sendRequest(req)
+	response, err := c.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
@@ -252,13 +209,13 @@ type AssetBalance struct {
 
 type AssetBalanceList []AssetBalance
 
-func (c *RestClient) AssetBalances() (AssetBalanceList, error) {
-	req, err := c.newAuthenticatedRequest("GET", "/api/v5/asset/balances", nil, nil)
+func (c *RestClient) AssetBalances(ctx context.Context) (AssetBalanceList, error) {
+	req, err := c.NewAuthenticatedRequest(ctx, "GET", "/api/v5/asset/balances", nil, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := c.sendRequest(req)
+	response, err := c.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
@@ -287,13 +244,13 @@ type AssetCurrency struct {
 	MinWithdrawalThreshold fixedpoint.Value `json:"minWd"`
 }
 
-func (c *RestClient) AssetCurrencies() ([]AssetCurrency, error) {
-	req, err := c.newAuthenticatedRequest("GET", "/api/v5/asset/currencies", nil, nil)
+func (c *RestClient) AssetCurrencies(ctx context.Context) ([]AssetCurrency, error) {
+	req, err := c.NewAuthenticatedRequest(ctx, "GET", "/api/v5/asset/currencies", nil, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := c.sendRequest(req)
+	response, err := c.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
@@ -337,17 +294,17 @@ type MarketTicker struct {
 	Timestamp types.MillisecondTimestamp `json:"ts"`
 }
 
-func (c *RestClient) MarketTicker(instId string) (*MarketTicker, error) {
+func (c *RestClient) MarketTicker(ctx context.Context, instId string) (*MarketTicker, error) {
 	// SPOT, SWAP, FUTURES, OPTION
 	var params = url.Values{}
 	params.Add("instId", instId)
 
-	req, err := c.newRequest("GET", "/api/v5/market/ticker", params, nil)
+	req, err := c.NewRequest(ctx, "GET", "/api/v5/market/ticker", params, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := c.sendRequest(req)
+	response, err := c.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
@@ -368,17 +325,17 @@ func (c *RestClient) MarketTicker(instId string) (*MarketTicker, error) {
 	return &tickerResponse.Data[0], nil
 }
 
-func (c *RestClient) MarketTickers(instType InstrumentType) ([]MarketTicker, error) {
+func (c *RestClient) MarketTickers(ctx context.Context, instType InstrumentType) ([]MarketTicker, error) {
 	// SPOT, SWAP, FUTURES, OPTION
 	var params = url.Values{}
 	params.Add("instType", string(instType))
 
-	req, err := c.newRequest("GET", "/api/v5/market/tickers", params, nil)
+	req, err := c.NewRequest(ctx, "GET", "/api/v5/market/tickers", params, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := c.sendRequest(req)
+	response, err := c.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
@@ -405,3 +362,9 @@ func Sign(payload string, secret string) string {
 	return base64.StdEncoding.EncodeToString(sig.Sum(nil))
 	// return hex.EncodeToString(sig.Sum(nil))
 }
+
+type APIResponse struct {
+	Code    string          `json:"code"`
+	Message string          `json:"msg"`
+	Data    json.RawMessage `json:"data"`
+}
diff --git a/pkg/exchange/okex/okexapi/client_test.go b/pkg/exchange/okex/okexapi/client_test.go
index ec6841642..8169450a9 100644
--- a/pkg/exchange/okex/okexapi/client_test.go
+++ b/pkg/exchange/okex/okexapi/client_test.go
@@ -22,17 +22,17 @@ func getTestClientOrSkip(t *testing.T) *RestClient {
 		return nil
 	}
 
-	client := NewClient()
+	client, err := NewClient()
+	assert.NoError(t, err)
 	client.Auth(key, secret, passphrase)
 	return client
 }
 
 func TestClient_GetInstrumentsRequest(t *testing.T) {
-	client := NewClient()
+	client, err := NewClient()
+	assert.NoError(t, err)
 	ctx := context.Background()
-
-	srv := &PublicDataService{client: client}
-	req := srv.NewGetInstrumentsRequest()
+	req := client.NewGetInstrumentsRequest()
 
 	instruments, err := req.
 		InstrumentType(InstrumentTypeSpot).
@@ -43,10 +43,10 @@ func TestClient_GetInstrumentsRequest(t *testing.T) {
 }
 
 func TestClient_GetFundingRateRequest(t *testing.T) {
-	client := NewClient()
+	client, err := NewClient()
+	assert.NoError(t, err)
 	ctx := context.Background()
-	srv := &PublicDataService{client: client}
-	req := srv.NewGetFundingRate()
+	req := client.NewGetFundingRate()
 
 	instrument, err := req.
 		InstrumentID("BTC-USDT-SWAP").
@@ -59,8 +59,7 @@ func TestClient_GetFundingRateRequest(t *testing.T) {
 func TestClient_PlaceOrderRequest(t *testing.T) {
 	client := getTestClientOrSkip(t)
 	ctx := context.Background()
-	srv := &TradeService{client: client}
-	req := srv.NewPlaceOrderRequest()
+	req := client.NewPlaceOrderRequest()
 
 	order, err := req.
 		InstrumentID("BTC-USDT").
@@ -78,8 +77,7 @@ func TestClient_PlaceOrderRequest(t *testing.T) {
 func TestClient_GetPendingOrderRequest(t *testing.T) {
 	client := getTestClientOrSkip(t)
 	ctx := context.Background()
-	srv := &TradeService{client: client}
-	req := srv.NewGetPendingOrderRequest()
+	req := client.NewGetPendingOrderRequest()
 	odr_type := []string{string(OrderTypeLimit), string(OrderTypeIOC)}
 
 	pending_order, err := req.
@@ -94,8 +92,7 @@ func TestClient_GetPendingOrderRequest(t *testing.T) {
 func TestClient_GetOrderDetailsRequest(t *testing.T) {
 	client := getTestClientOrSkip(t)
 	ctx := context.Background()
-	srv := &TradeService{client: client}
-	req := srv.NewGetOrderDetailsRequest()
+	req := client.NewGetOrderDetailsRequest()
 
 	orderDetail, err := req.
 		InstrumentID("BTC-USDT").
diff --git a/pkg/exchange/okex/okexapi/market.go b/pkg/exchange/okex/okexapi/market.go
index b9b46c43f..9c5b7d0db 100644
--- a/pkg/exchange/okex/okexapi/market.go
+++ b/pkg/exchange/okex/okexapi/market.go
@@ -2,6 +2,7 @@ package okexapi
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"net/url"
 	"strconv"
@@ -82,29 +83,29 @@ func (r *CandlesticksRequest) Do(ctx context.Context) ([]Candle, error) {
 		params.Add("limit", strconv.Itoa(*r.limit))
 	}
 
-	req, err := r.client.newRequest("GET", "/api/v5/market/candles", params, nil)
+	req, err := r.client.NewRequest(ctx, "GET", "/api/v5/market/candles", params, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	resp, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
 	type candleEntry [7]string
-	var candlesResponse struct {
-		Code    string        `json:"code"`
-		Message string        `json:"msg"`
-		Data    []candleEntry `json:"data"`
-	}
 
-	if err := resp.DecodeJSON(&candlesResponse); err != nil {
+	var apiResponse APIResponse
+	if err := response.DecodeJSON(&apiResponse); err != nil {
+		return nil, err
+	}
+	var data []candleEntry
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
 		return nil, err
 	}
 
 	var candles []Candle
-	for _, entry := range candlesResponse.Data {
+	for _, entry := range data {
 		timestamp, err := strconv.ParseInt(entry[0], 10, 64)
 		if err != nil {
 			return candles, err
@@ -177,27 +178,26 @@ func (r *MarketTickersRequest) Do(ctx context.Context) ([]MarketTicker, error) {
 	var params = url.Values{}
 	params.Add("instType", string(r.instType))
 
-	req, err := r.client.newRequest("GET", "/api/v5/market/tickers", params, nil)
+	req, err := r.client.NewRequest(ctx, "GET", "/api/v5/market/tickers", params, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var tickerResponse struct {
-		Code    string         `json:"code"`
-		Message string         `json:"msg"`
-		Data    []MarketTicker `json:"data"`
+	var apiResponse APIResponse
+	if err := response.DecodeJSON(&apiResponse); err != nil {
+		return nil, err
 	}
-
-	if err := response.DecodeJSON(&tickerResponse); err != nil {
+	var data []MarketTicker
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
 		return nil, err
 	}
 
-	return tickerResponse.Data, nil
+	return data, nil
 }
 
 type MarketTickerRequest struct {
@@ -216,53 +216,49 @@ func (r *MarketTickerRequest) Do(ctx context.Context) (*MarketTicker, error) {
 	var params = url.Values{}
 	params.Add("instId", r.instId)
 
-	req, err := r.client.newRequest("GET", "/api/v5/market/ticker", params, nil)
+	req, err := r.client.NewRequest(ctx, "GET", "/api/v5/market/ticker", params, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var tickerResponse struct {
-		Code    string         `json:"code"`
-		Message string         `json:"msg"`
-		Data    []MarketTicker `json:"data"`
+	var apiResponse APIResponse
+	if err := response.DecodeJSON(&apiResponse); err != nil {
+		return nil, err
 	}
-	if err := response.DecodeJSON(&tickerResponse); err != nil {
+	var data []MarketTicker
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
 		return nil, err
 	}
 
-	if len(tickerResponse.Data) == 0 {
+	if len(data) == 0 {
 		return nil, fmt.Errorf("ticker of %s not found", r.instId)
 	}
 
-	return &tickerResponse.Data[0], nil
+	return &data[0], nil
 }
 
-type MarketDataService struct {
-	client *RestClient
-}
-
-func (c *MarketDataService) NewMarketTickerRequest(instId string) *MarketTickerRequest {
+func (c *RestClient) NewMarketTickerRequest(instId string) *MarketTickerRequest {
 	return &MarketTickerRequest{
-		client: c.client,
+		client: c,
 		instId: instId,
 	}
 }
 
-func (c *MarketDataService) NewMarketTickersRequest(instType string) *MarketTickersRequest {
+func (c *RestClient) NewMarketTickersRequest(instType string) *MarketTickersRequest {
 	return &MarketTickersRequest{
-		client:   c.client,
+		client:   c,
 		instType: instType,
 	}
 }
 
-func (c *MarketDataService) NewCandlesticksRequest(instId string) *CandlesticksRequest {
+func (c *RestClient) NewCandlesticksRequest(instId string) *CandlesticksRequest {
 	return &CandlesticksRequest{
-		client: c.client,
+		client: c,
 		instId: instId,
 	}
 }
diff --git a/pkg/exchange/okex/okexapi/public.go b/pkg/exchange/okex/okexapi/public.go
index b877fe637..af4b45496 100644
--- a/pkg/exchange/okex/okexapi/public.go
+++ b/pkg/exchange/okex/okexapi/public.go
@@ -2,6 +2,7 @@ package okexapi
 
 import (
 	"context"
+	"encoding/json"
 	"net/url"
 
 	"github.com/c9s/bbgo/pkg/fixedpoint"
@@ -9,19 +10,15 @@ import (
 	"github.com/pkg/errors"
 )
 
-type PublicDataService struct {
-	client *RestClient
-}
-
-func (s *PublicDataService) NewGetInstrumentsRequest() *GetInstrumentsRequest {
+func (s *RestClient) NewGetInstrumentsRequest() *GetInstrumentsRequest {
 	return &GetInstrumentsRequest{
-		client: s.client,
+		client: s,
 	}
 }
 
-func (s *PublicDataService) NewGetFundingRate() *GetFundingRateRequest {
+func (s *RestClient) NewGetFundingRate() *GetFundingRateRequest {
 	return &GetFundingRateRequest{
-		client: s.client,
+		client: s,
 	}
 }
 
@@ -49,30 +46,30 @@ func (r *GetFundingRateRequest) Do(ctx context.Context) (*FundingRate, error) {
 	var params = url.Values{}
 	params.Add("instId", string(r.instId))
 
-	req, err := r.client.newRequest("GET", "/api/v5/public/funding-rate", params, nil)
+	req, err := r.client.NewRequest(ctx, "GET", "/api/v5/public/funding-rate", params, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var apiResponse struct {
-		Code    string        `json:"code"`
-		Message string        `json:"msg"`
-		Data    []FundingRate `json:"data"`
-	}
+	var apiResponse APIResponse
 	if err := response.DecodeJSON(&apiResponse); err != nil {
 		return nil, err
 	}
+	var data []FundingRate
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
+		return nil, err
+	}
 
-	if len(apiResponse.Data) == 0 {
+	if len(data) == 0 {
 		return nil, errors.New("empty funding rate data")
 	}
 
-	return &apiResponse.Data[0], nil
+	return &data[0], nil
 }
 
 type Instrument struct {
@@ -123,24 +120,24 @@ func (r *GetInstrumentsRequest) Do(ctx context.Context) ([]Instrument, error) {
 		params.Add("instId", *r.instId)
 	}
 
-	req, err := r.client.newRequest("GET", "/api/v5/public/instruments", params, nil)
+	req, err := r.client.NewRequest(ctx, "GET", "/api/v5/public/instruments", params, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var apiResponse struct {
-		Code    string       `json:"code"`
-		Message string       `json:"msg"`
-		Data    []Instrument `json:"data"`
-	}
+	var apiResponse APIResponse
 	if err := response.DecodeJSON(&apiResponse); err != nil {
 		return nil, err
 	}
+	var data []Instrument
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
+		return nil, err
+	}
 
-	return apiResponse.Data, nil
+	return data, nil
 }
diff --git a/pkg/exchange/okex/okexapi/trade.go b/pkg/exchange/okex/okexapi/trade.go
index 8a814057b..4c0ecf26a 100644
--- a/pkg/exchange/okex/okexapi/trade.go
+++ b/pkg/exchange/okex/okexapi/trade.go
@@ -2,6 +2,7 @@ package okexapi
 
 import (
 	"context"
+	"encoding/json"
 	"net/url"
 	"strings"
 
@@ -10,10 +11,6 @@ import (
 	"github.com/pkg/errors"
 )
 
-type TradeService struct {
-	client *RestClient
-}
-
 type OrderResponse struct {
 	OrderID       string `json:"ordId"`
 	ClientOrderID string `json:"clOrdId"`
@@ -22,45 +19,45 @@ type OrderResponse struct {
 	Message       string `json:"sMsg"`
 }
 
-func (c *TradeService) NewPlaceOrderRequest() *PlaceOrderRequest {
+func (c *RestClient) NewPlaceOrderRequest() *PlaceOrderRequest {
 	return &PlaceOrderRequest{
-		client: c.client,
+		client: c,
 	}
 }
 
-func (c *TradeService) NewBatchPlaceOrderRequest() *BatchPlaceOrderRequest {
+func (c *RestClient) NewBatchPlaceOrderRequest() *BatchPlaceOrderRequest {
 	return &BatchPlaceOrderRequest{
-		client: c.client,
+		client: c,
 	}
 }
 
-func (c *TradeService) NewCancelOrderRequest() *CancelOrderRequest {
+func (c *RestClient) NewCancelOrderRequest() *CancelOrderRequest {
 	return &CancelOrderRequest{
-		client: c.client,
+		client: c,
 	}
 }
 
-func (c *TradeService) NewBatchCancelOrderRequest() *BatchCancelOrderRequest {
+func (c *RestClient) NewBatchCancelOrderRequest() *BatchCancelOrderRequest {
 	return &BatchCancelOrderRequest{
-		client: c.client,
+		client: c,
 	}
 }
 
-func (c *TradeService) NewGetOrderDetailsRequest() *GetOrderDetailsRequest {
+func (c *RestClient) NewGetOrderDetailsRequest() *GetOrderDetailsRequest {
 	return &GetOrderDetailsRequest{
-		client: c.client,
+		client: c,
 	}
 }
 
-func (c *TradeService) NewGetPendingOrderRequest() *GetPendingOrderRequest {
+func (c *RestClient) NewGetPendingOrderRequest() *GetPendingOrderRequest {
 	return &GetPendingOrderRequest{
-		client: c.client,
+		client: c,
 	}
 }
 
-func (c *TradeService) NewGetTransactionDetailsRequest() *GetTransactionDetailsRequest {
+func (c *RestClient) NewGetTransactionDetailsRequest() *GetTransactionDetailsRequest {
 	return &GetTransactionDetailsRequest{
-		client: c.client,
+		client: c,
 	}
 }
 
@@ -99,30 +96,30 @@ func (r *PlaceOrderRequest) Parameters() map[string]interface{} {
 
 func (r *PlaceOrderRequest) Do(ctx context.Context) (*OrderResponse, error) {
 	payload := r.Parameters()
-	req, err := r.client.newAuthenticatedRequest("POST", "/api/v5/trade/order", nil, payload)
+	req, err := r.client.NewAuthenticatedRequest(ctx, "POST", "/api/v5/trade/order", nil, payload)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var orderResponse struct {
-		Code    string          `json:"code"`
-		Message string          `json:"msg"`
-		Data    []OrderResponse `json:"data"`
+	var apiResponse APIResponse
+	if err := response.DecodeJSON(&apiResponse); err != nil {
+		return nil, err
 	}
-	if err := response.DecodeJSON(&orderResponse); err != nil {
+	var data []OrderResponse
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
 		return nil, err
 	}
 
-	if len(orderResponse.Data) == 0 {
+	if len(data) == 0 {
 		return nil, errors.New("order create error")
 	}
 
-	return &orderResponse.Data[0], nil
+	return &data[0], nil
 }
 
 //go:generate requestgen -type CancelOrderRequest
@@ -149,26 +146,26 @@ func (r *CancelOrderRequest) Do(ctx context.Context) ([]OrderResponse, error) {
 		return nil, errors.New("either orderID or clientOrderID is required for canceling order")
 	}
 
-	req, err := r.client.newAuthenticatedRequest("POST", "/api/v5/trade/cancel-order", nil, payload)
+	req, err := r.client.NewAuthenticatedRequest(ctx, "POST", "/api/v5/trade/cancel-order", nil, payload)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var orderResponse struct {
-		Code    string          `json:"code"`
-		Message string          `json:"msg"`
-		Data    []OrderResponse `json:"data"`
+	var apiResponse APIResponse
+	if err := response.DecodeJSON(&apiResponse); err != nil {
+		return nil, err
 	}
-	if err := response.DecodeJSON(&orderResponse); err != nil {
+	var data []OrderResponse
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
 		return nil, err
 	}
 
-	return orderResponse.Data, nil
+	return data, nil
 }
 
 type BatchCancelOrderRequest struct {
@@ -190,26 +187,26 @@ func (r *BatchCancelOrderRequest) Do(ctx context.Context) ([]OrderResponse, erro
 		parameterList = append(parameterList, params)
 	}
 
-	req, err := r.client.newAuthenticatedRequest("POST", "/api/v5/trade/cancel-batch-orders", nil, parameterList)
+	req, err := r.client.NewAuthenticatedRequest(ctx, "POST", "/api/v5/trade/cancel-batch-orders", nil, parameterList)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var orderResponse struct {
-		Code    string          `json:"code"`
-		Message string          `json:"msg"`
-		Data    []OrderResponse `json:"data"`
+	var apiResponse APIResponse
+	if err := response.DecodeJSON(&apiResponse); err != nil {
+		return nil, err
 	}
-	if err := response.DecodeJSON(&orderResponse); err != nil {
+	var data []OrderResponse
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
 		return nil, err
 	}
 
-	return orderResponse.Data, nil
+	return data, nil
 }
 
 type BatchPlaceOrderRequest struct {
@@ -231,26 +228,26 @@ func (r *BatchPlaceOrderRequest) Do(ctx context.Context) ([]OrderResponse, error
 		parameterList = append(parameterList, params)
 	}
 
-	req, err := r.client.newAuthenticatedRequest("POST", "/api/v5/trade/batch-orders", nil, parameterList)
+	req, err := r.client.NewAuthenticatedRequest(ctx, "POST", "/api/v5/trade/batch-orders", nil, parameterList)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var orderResponse struct {
-		Code    string          `json:"code"`
-		Message string          `json:"msg"`
-		Data    []OrderResponse `json:"data"`
+	var apiResponse APIResponse
+	if err := response.DecodeJSON(&apiResponse); err != nil {
+		return nil, err
 	}
-	if err := response.DecodeJSON(&orderResponse); err != nil {
+	var data []OrderResponse
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
 		return nil, err
 	}
 
-	return orderResponse.Data, nil
+	return data, nil
 }
 
 type OrderDetails struct {
@@ -343,30 +340,30 @@ func (r *GetOrderDetailsRequest) QueryParameters() url.Values {
 
 func (r *GetOrderDetailsRequest) Do(ctx context.Context) (*OrderDetails, error) {
 	params := r.QueryParameters()
-	req, err := r.client.newAuthenticatedRequest("GET", "/api/v5/trade/order", params, nil)
+	req, err := r.client.NewAuthenticatedRequest(ctx, "GET", "/api/v5/trade/order", params, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var orderResponse struct {
-		Code    string         `json:"code"`
-		Message string         `json:"msg"`
-		Data    []OrderDetails `json:"data"`
+	var apiResponse APIResponse
+	if err := response.DecodeJSON(&apiResponse); err != nil {
+		return nil, err
 	}
-	if err := response.DecodeJSON(&orderResponse); err != nil {
+	var data []OrderDetails
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
 		return nil, err
 	}
 
-	if len(orderResponse.Data) == 0 {
+	if len(data) == 0 {
 		return nil, errors.New("get order details error")
 	}
 
-	return &orderResponse.Data[0], nil
+	return &data[0], nil
 }
 
 type GetPendingOrderRequest struct {
@@ -430,26 +427,26 @@ func (r *GetPendingOrderRequest) Parameters() map[string]interface{} {
 
 func (r *GetPendingOrderRequest) Do(ctx context.Context) ([]OrderDetails, error) {
 	payload := r.Parameters()
-	req, err := r.client.newAuthenticatedRequest("GET", "/api/v5/trade/orders-pending", nil, payload)
+	req, err := r.client.NewAuthenticatedRequest(ctx, "GET", "/api/v5/trade/orders-pending", nil, payload)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var orderResponse struct {
-		Code    string         `json:"code"`
-		Message string         `json:"msg"`
-		Data    []OrderDetails `json:"data"`
+	var apiResponse APIResponse
+	if err := response.DecodeJSON(&apiResponse); err != nil {
+		return nil, err
 	}
-	if err := response.DecodeJSON(&orderResponse); err != nil {
+	var data []OrderDetails
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
 		return nil, err
 	}
 
-	return orderResponse.Data, nil
+	return data, nil
 }
 
 type GetTransactionDetailsRequest struct {
@@ -497,24 +494,24 @@ func (r *GetTransactionDetailsRequest) Parameters() map[string]interface{} {
 
 func (r *GetTransactionDetailsRequest) Do(ctx context.Context) ([]OrderDetails, error) {
 	payload := r.Parameters()
-	req, err := r.client.newAuthenticatedRequest("GET", "/api/v5/trade/fills", nil, payload)
+	req, err := r.client.NewAuthenticatedRequest(ctx, "GET", "/api/v5/trade/fills", nil, payload)
 	if err != nil {
 		return nil, err
 	}
 
-	response, err := r.client.sendRequest(req)
+	response, err := r.client.SendRequest(req)
 	if err != nil {
 		return nil, err
 	}
 
-	var orderResponse struct {
-		Code    string         `json:"code"`
-		Message string         `json:"msg"`
-		Data    []OrderDetails `json:"data"`
+	var apiResponse APIResponse
+	if err := response.DecodeJSON(&apiResponse); err != nil {
+		return nil, err
 	}
-	if err := response.DecodeJSON(&orderResponse); err != nil {
+	var data []OrderDetails
+	if err := json.Unmarshal(apiResponse.Data, &data); err != nil {
 		return nil, err
 	}
 
-	return orderResponse.Data, nil
+	return data, nil
 }
diff --git a/pkg/exchange/okex/query_order_test.go b/pkg/exchange/okex/query_order_test.go
index 3c32da40c..025e045ba 100644
--- a/pkg/exchange/okex/query_order_test.go
+++ b/pkg/exchange/okex/query_order_test.go
@@ -22,7 +22,8 @@ func Test_QueryOrder(t *testing.T) {
 		return
 	}
 
-	e := New(key, secret, passphrase)
+	e, err := New(key, secret, passphrase)
+	assert.NoError(t, err)
 
 	queryOrder := types.OrderQuery{
 		Symbol:  "BTC-USDT",