diff --git a/src/layer.js b/src/layer.js
index 9c75351..d1117db 100644
--- a/src/layer.js
+++ b/src/layer.js
@@ -1072,7 +1072,7 @@ layer.prompt = function(options, yes){
       var value = prompt.val();
       if(value === ''){
         prompt.focus();
-      } else if(value.length > (options.maxlength||500)) {
+      } else if(value&&value.length > (options.maxlength||500)) {
         layer.tips('最多输入'+ (options.maxlength || 500) +'个字数', prompt, {tips: 1});
       } else {
         yes && yes(value, index, prompt);