diff --git a/ios/sdk/WeexSDK/Sources/Utility/WXUtility.m b/ios/sdk/WeexSDK/Sources/Utility/WXUtility.m
index b070a87baf..2e6f9a7243 100644
--- a/ios/sdk/WeexSDK/Sources/Utility/WXUtility.m
+++ b/ios/sdk/WeexSDK/Sources/Utility/WXUtility.m
@@ -846,6 +846,10 @@ + (NSString *)stringWithContentsOfFile:(NSString *)filePath
 + (NSString *)md5:(NSString *)string
 {
     const char *str = string.UTF8String;
+    if (str == NULL) {
+        return nil;
+    }
+    
     unsigned char result[CC_MD5_DIGEST_LENGTH];
     CC_MD5(str, (CC_LONG)strlen(str), result);