diff --git a/src/layer.js b/src/layer.js
index e906069..12061ed 100644
--- a/src/layer.js
+++ b/src/layer.js
@@ -1003,7 +1003,7 @@ layer.prompt = function(options, yes){
     ,resize: false
     ,yes: function(index){
       var value = prompt.val();
-      if(value === ''){
+      if(!options.allowNull && value === ''){
         prompt.focus();
       } else if(value.length > (options.maxlength||500)) {
         layer.tips('最多输入'+ (options.maxlength || 500) +'个字数', prompt, {tips: 1});