diff --git a/Gruntfile.js b/Gruntfile.js
index 347b0c705..f525b02f8 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -250,7 +250,7 @@ module.exports = function (grunt) {
         },
         watch: {
             scripts: {
-                files: ["src/**/*.js", "demo/js/**/*.js", "demo/version.js", "demo/config.js", "demo/less/**/*.less"],
+                files: ["src/**/*", "demo/js/**/*.js", "demo/version.js", "demo/config.js", "demo/less/**/*.less"],
                 tasks: ["less", "concat"],
                 options: {
                     spanw: true,
@@ -278,7 +278,8 @@ module.exports = function (grunt) {
                     base: "./dist"
                 }
             }
-        }
+        },
+        clean: ["src/css", "demo/css"]
     });
 
     grunt.loadNpmTasks("grunt-contrib-uglify");
@@ -288,13 +289,14 @@ module.exports = function (grunt) {
     grunt.loadNpmTasks("grunt-contrib-concat");
     grunt.loadNpmTasks("grunt-contrib-cssmin");
     grunt.loadNpmTasks("grunt-contrib-connect");
+    grunt.loadNpmTasks('grunt-contrib-clean');
 
-    var defaultTask = ["less", "concat", "connect", "watch"];
+    var defaultTask = ["clean", "less", "concat", "connect", "watch"];
     grunt.registerTask("default", defaultTask);
     grunt.registerTask("compile", function () {
         grunt.config.set("connect.options.open", false);
         grunt.task.run(defaultTask);
     });
-    grunt.registerTask("min", ["less", "concat", "uglify", "cssmin"]);
-    grunt.registerTask("build", ["less", "concat", "uglify", "cssmin", "uglify", "concat"]);
+    grunt.registerTask("min", ["clean", "less", "concat", "uglify", "cssmin"]);
+    grunt.registerTask("build", ["clean", "less", "concat", "uglify", "cssmin", "uglify", "concat"]);
 };
diff --git a/package-lock.json b/package-lock.json
index f04d557de..c3ffb84e3 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1020,6 +1020,27 @@
         }
       }
     },
+    "grunt-contrib-clean": {
+      "version": "1.1.0",
+      "resolved": "http://r.cnpmjs.org/grunt-contrib-clean/download/grunt-contrib-clean-1.1.0.tgz",
+      "integrity": "sha1-Vkq/LQN4qYOhW54/MO51tzjEBjg=",
+      "dev": true,
+      "requires": {
+        "async": "^1.5.2",
+        "rimraf": "^2.5.1"
+      },
+      "dependencies": {
+        "rimraf": {
+          "version": "2.6.2",
+          "resolved": "http://r.cnpmjs.org/rimraf/download/rimraf-2.6.2.tgz",
+          "integrity": "sha1-LtgVDSShbqhlHm1u8PR8QVjOejY=",
+          "dev": true,
+          "requires": {
+            "glob": "^7.0.5"
+          }
+        }
+      }
+    },
     "grunt-contrib-concat": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/grunt-contrib-concat/-/grunt-contrib-concat-1.0.1.tgz",
diff --git a/package.json b/package.json
index 951dee150..e5721211c 100644
--- a/package.json
+++ b/package.json
@@ -7,6 +7,7 @@
   "devDependencies": {
     "express": "^4.15.2",
     "grunt": "^1.0.1",
+    "grunt-contrib-clean": "^1.1.0",
     "grunt-contrib-concat": "^1.0.1",
     "grunt-contrib-connect": "^1.0.2",
     "grunt-contrib-cssmin": "^1.0.1",