diff --git a/zh-cn/application-dev/security/cryptoFramework-guidelines.md b/zh-cn/application-dev/security/cryptoFramework-guidelines.md
index ceebac4892ce465afe1302f14445d9e14785687d..6083a26fd1495f1a6bbe85e617061bc9d17b0164 100644
--- a/zh-cn/application-dev/security/cryptoFramework-guidelines.md
+++ b/zh-cn/application-dev/security/cryptoFramework-guidelines.md
@@ -351,7 +351,7 @@ function testGenerateHmacKey() {
 ```ts
 import cryptoFramework from '@ohos.security.cryptoFramework';
 
-function stringToUint8Array(str) {
+function stringToUint8Array(str: string) {
   let arr = [];
   for (let i = 0, j = str.length; i < j; ++i) {
     arr.push(str.charCodeAt(i));