下载异步上传插件AjaxFileUploader，下载地址：http://phpletter.com/DOWNLOAD/

解压，保存在 asp.net mvc项目的一个文件夹下，如下图：
1.         Controller层
 public ActionResult View3()
        {
            return View();
 
        }
        [HttpPost]
        public ActionResult View3(HttpPostedFileBase file)
        {
            if (file == null)
            {
                return Content("没有文件！", "text/plain");
            }
            var fileName = Path.Combine(Request.MapPath("~/UploadFiles"), Path.GetFileName(file.FileName));
            try
            {
                file.SaveAs(fileName);             
                return Content("上传成功！", "text/plain");
            }
            catch
            {
                return Content("上传异常 ！", "text/plain");
            }
        }
 
2.         View层：
@{
    Layout = null;
}
 
<!DOCTYPE html>
 
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>View1</title>
    <script src="~/Scripts/jquery-1.7.1.min.js"></script>
   
    <script src="~/ajaxfileupload/jquery.js"></script>
    <script src="~/ajaxfileupload/ajaxfileupload.js"></script>
    <script type="text/javascript">
        function ajaxFileUploads() {
            $("#loading").ajaxStart(function () {
                $(this).show();
            })//开始上传文件时显示一个图片
               .ajaxComplete(function () {
                   $(this).hide();
               });//文件上传完成将图片隐藏起来
 
            $.ajaxFileUpload({
                url: '/Test/View3',//后台处理的action
                secureuri: false,
                fileElementId: 'file',//上传的控件名
                dataType: 'text',
                success: function (data, status) {
                    $("#mydiv").html( data);
                },
                error: function (data, status, e) {
                    $("#mydiv").html( data + "   " + e);
                }
            })
            return false;
        }
    </script>
</head>
<body>
    <input type="file" id="file" name="file" />
    <img src="../ajaxfileupload/loading.gif" width="20px" height="20px" id="loading" style="display: none;">
    <span id="mydiv" style="color: green;"></span>
    <br />
    <input type="button" value="上传" ajaxFileUploads();">
</body>
</html>