diff --git a/backend/verifyCode/cmd/verifyCode/main.go b/backend/verifyCode/cmd/verifyCode/main.go
index 4830be6..de7593f 100644
--- a/backend/verifyCode/cmd/verifyCode/main.go
+++ b/backend/verifyCode/cmd/verifyCode/main.go
@@ -2,7 +2,9 @@ package main
 
 import (
 	"flag"
+	"math/rand"
 	"os"
+	"time"
 
 	"verifyCode/internal/conf"
 
@@ -79,7 +81,8 @@ func main() {
 		panic(err)
 	}
 	defer cleanup()
-
+	//set rand seed
+	rand.Seed(time.Now().UnixNano())
 	// start and wait for stop signal
 	if err := app.Run(); err != nil {
 		panic(err)
diff --git a/backend/verifyCode/internal/service/verifycode.go b/backend/verifyCode/internal/service/verifycode.go
index 27e0748..128583e 100644
--- a/backend/verifyCode/internal/service/verifycode.go
+++ b/backend/verifyCode/internal/service/verifycode.go
@@ -3,7 +3,6 @@ package service
 import (
 	"context"
 	"math/rand"
-
 	pb "verifyCode/api/verifyCode"
 )
 
@@ -27,24 +26,56 @@ func RandCode(l int, r pb.TYPE) string {
 
 		fallthrough
 	case pb.TYPE_DIGIT:
-		return randcode("0123456789", l)
+		return randcode("0123456789", l, 4)
 	case pb.TYPE_LETTRE:
-		return randcode("abcdefghigklmnopqrstuvwxyz", l)
+		return randcode("abcdefghigklmnopqrstuvwxyz", l, 5)
 	case pb.TYPE_MIXED:
-		return randcode("0123456789abcdefghigklmnopqrstuvwxyz", l)
+		return randcode("0123456789abcdefghigklmnopqrstuvwxyz", l, 6)
 	default:
-
+		return ""
 	}
-	return ""
 }
 
-// 随机的核心方法
-func randcode(chars string, l int) string {
-	charsLen := len(chars)
+// 随机数和新方法：优化实现
+// 一次随机多次使用，分部分多次使用
+func randcode(chars string, l, idxBits int) string {
+	//计算有效的二进制数，基于char的长度
+	//推荐写死，chars固定，idxBits固定
+
+	//形成掩码。mask
+	//例如，使用低六位：00000000000111111
+	idxMask := 1<<idxBits - 1 //00001000000 - 1 = 00000111111
+	//63位可以使用多少次
+	idxMax := 63 / idxBits
+	//结果
 	result := make([]byte, l)
-	for i := 0; i < l; i++ {
-		randIndex := rand.Intn(charsLen)
-		result[i] = chars[randIndex]
+	//生成随机数
+	//cache:随机位缓存
+	//remain:还可以用多少次
+	for i, cache, remain := 0, rand.Int63(), idxMax; i < l; {
+		if remain == 0 {
+			cache, remain = rand.Int63(), idxMax
+		}
+		//利用掩码获取有效位的随机数
+		if randIndex := int(cache & int64(idxMask)); randIndex < len(chars) {
+			result[i] = chars[randIndex]
+			i++
+		}
+		//使用下一组随即位
+		cache >>= idxBits
+		//减少一次使用次数
+		remain--
 	}
 	return string(result)
 }
+
+// 随机的核心方法:简单实现
+//func randcode(chars string, l int) string {
+//	charsLen := len(chars)
+//	result := make([]byte, l)
+//	for i := 0; i < l; i++ {
+//		randIndex := rand.Intn(charsLen)
+//		result[i] = chars[randIndex]
+//	}
+//	return string(result)
+//}