diff --git a/cli/hrp/cmd/har2case.go b/cli/hrp/cmd/har2case.go
index c59ac313..30f8f618 100644
--- a/cli/hrp/cmd/har2case.go
+++ b/cli/hrp/cmd/har2case.go
@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"errors"
 	"github.com/rs/zerolog/log"
 	"github.com/spf13/cobra"
 
@@ -19,6 +20,10 @@ var har2caseCmd = &cobra.Command{
 	RunE: func(cmd *cobra.Command, args []string) error {
 		var outputFiles []string
 		for _, arg := range args {
+			// must choose one
+			if !genYAMLFlag && !genJSONFlag {
+				return errors.New("please select to-json flag or to-yaml flag.")
+			}
 			var outputPath string
 			var err error
 
@@ -28,7 +33,6 @@ var har2caseCmd = &cobra.Command{
 			if outputDir != "" {
 				har.SetOutputDir(outputDir)
 			}
-
 			// generate json/yaml files
 			if genYAMLFlag {
 				outputPath, err = har.GenYAML()
@@ -53,7 +57,7 @@ var (
 
 func init() {
 	rootCmd.AddCommand(har2caseCmd)
-	har2caseCmd.Flags().BoolVarP(&genJSONFlag, "to-json", "j", false, "convert to JSON format (default)")
-	har2caseCmd.Flags().BoolVarP(&genYAMLFlag, "to-yaml", "y", false, "convert to JSON format")
+	har2caseCmd.Flags().BoolVarP(&genJSONFlag, "to-json", "j", true, "convert to JSON format")
+	har2caseCmd.Flags().BoolVarP(&genYAMLFlag, "to-yaml", "y", false, "convert to YAML format")
 	har2caseCmd.Flags().StringVarP(&outputDir, "output-dir", "d", "", "specify output directory, default to the same dir with har file")
 }