diff --git a/boomer.go b/boomer.go
index 48593fbd..7096aee9 100644
--- a/boomer.go
+++ b/boomer.go
@@ -1,6 +1,7 @@
 package hrp
 
 import (
+	"github.com/jinzhu/copier"
 	"time"
 
 	"github.com/rs/zerolog/log"
@@ -69,12 +70,17 @@ func (b *hrpBoomer) convertBoomerTask(testcase *TestCase) *boomer.Task {
 			var transactionSuccess = true // flag current transaction result
 
 			cfg := testcase.Config.ToStruct()
+			testCaseVariables := &TConfig{}
+			// copy config to avoid data racing
+			if err := copier.Copy(testCaseVariables, cfg); err != nil {
+				log.Error().Err(err).Msg("copy config data failed")
+			}
 			if it := cfg.ParametersSetting.Iterator; it.HasNext() {
-				cfg.Variables = mergeVariables(it.Next(), cfg.Variables)
+				testCaseVariables.Variables = mergeVariables(it.Next(), cfg.Variables)
 			}
 			startTime := time.Now()
 			for index, step := range testcase.TestSteps {
-				stepData, err := runner.runStep(index)
+				stepData, err := runner.runStep(index, testCaseVariables)
 				if err != nil {
 					// step failed
 					var elapsed int64
diff --git a/runner.go b/runner.go
index c227064a..df33b966 100644
--- a/runner.go
+++ b/runner.go
@@ -147,7 +147,7 @@ func (r *caseRunner) run() error {
 		cfg.Variables = mergeVariables(it.Next(), cfg.Variables)
 		r.startTime = time.Now()
 		for index := range r.TestCase.TestSteps {
-			_, err := r.runStep(index)
+			_, err := r.runStep(index, cfg)
 			if err != nil {
 				if r.hrpRunner.failfast {
 					return errors.Wrap(err, "abort running due to failfast setting")
@@ -160,8 +160,7 @@ func (r *caseRunner) run() error {
 	return nil
 }
 
-func (r *caseRunner) runStep(index int) (stepResult *stepData, err error) {
-	config := r.TestCase.Config
+func (r *caseRunner) runStep(index int, caseConfig *TConfig) (stepResult *stepData, err error) {
 	step := r.TestCase.TestSteps[index]
 
 	// step type priority order: transaction > rendezvous > testcase > request
@@ -181,23 +180,18 @@ func (r *caseRunner) runStep(index int) (stepResult *stepData, err error) {
 		log.Error().Err(err).Msg("copy step data failed")
 		return nil, err
 	}
-	copiedConfig := &TConfig{}
-	if err = copier.Copy(copiedConfig, config.ToStruct()); err != nil {
-		log.Error().Err(err).Msg("copy config data failed")
-		return nil, err
-	}
 
 	stepVariables := copiedStep.Variables
 	// override variables
 	// step variables > session variables (extracted variables from previous steps)
 	stepVariables = mergeVariables(stepVariables, r.sessionVariables)
 	// step variables > testcase config variables
-	stepVariables = mergeVariables(stepVariables, copiedConfig.Variables)
+	stepVariables = mergeVariables(stepVariables, caseConfig.Variables)
 
 	// parse step variables
 	parsedVariables, err := parseVariables(stepVariables)
 	if err != nil {
-		log.Error().Interface("variables", copiedConfig.Variables).Err(err).Msg("parse step variables failed")
+		log.Error().Interface("variables", caseConfig.Variables).Err(err).Msg("parse step variables failed")
 		return nil, err
 	}
 	copiedStep.Variables = parsedVariables // avoid data racing
@@ -214,7 +208,7 @@ func (r *caseRunner) runStep(index int) (stepResult *stepData, err error) {
 		}
 	} else {
 		// run request
-		copiedStep.Request.URL = buildURL(copiedConfig.BaseURL, copiedStep.Request.URL) // avoid data racing
+		copiedStep.Request.URL = buildURL(caseConfig.BaseURL, copiedStep.Request.URL) // avoid data racing
 		stepResult, err = r.runStepRequest(copiedStep)
 		if err != nil {
 			log.Error().Err(err).Msg("run request step failed")
diff --git a/step_test.go b/step_test.go
index 5fdd3c02..d7e3ee17 100644
--- a/step_test.go
+++ b/step_test.go
@@ -79,10 +79,10 @@ func TestRunRequestRun(t *testing.T) {
 		TestSteps: []IStep{stepGET, stepPOSTData},
 	}
 	runner := NewRunner(t).SetDebug(true).newCaseRunner(testcase)
-	if _, err := runner.runStep(0); err != nil {
+	if _, err := runner.runStep(0, testcase.Config.ToStruct()); err != nil {
 		t.Fatalf("tStep.Run() error: %s", err)
 	}
-	if _, err := runner.runStep(1); err != nil {
+	if _, err := runner.runStep(1, testcase.Config.ToStruct()); err != nil {
 		t.Fatalf("tStepPOSTData.Run() error: %s", err)
 	}
 }