<form id="uploadForm" enctype="multipart/form-data" action="/Login/uploadFile" method="post">
 <input type="file" multiple="multiple" id="PersonFile" name="MyFile" />
 <button type="button" id="submitFile" onclick="uploadFile()">提交</button>
</form>

//上传文件
 function uploadFile() {
  debugger
  $.ajax({
  url: '/Login/uploadFile',
  type: 'POST',
  cache: false,
  data: new FormData($('#uploadForm')[0]),
  processData: false, // 关键点
  contentType: false, // 关键点
  success: function (result) {
   if (result.Check) {
   alert("成功");
   }
   else {
   alert("失败");
   }
   var file = $("#PersonFile")
   file.after(file.clone().val(""));
   file.remove();
  }
  });
 }

 [HttpPost]
 public ActionResult uploadFile()
 {
  Result<string> check = new Result<string>();
  try
  {
  HttpFileCollection files = System.Web.HttpContext.Current.Request.Files;
  int number = 0;
  for (int i = 0; i < files.Count; i++)
  {
   System.Text.StringBuilder fileName = new System.Text.StringBuilder();
   fileName.Append(@"D:\");
   fileName.Append(DateTime.Now.ToString("yyMMdd"));
   fileName.Append(@"\");
   if (!System.IO.Directory.Exists(fileName.ToString()))
   {
   System.IO.Directory.CreateDirectory(fileName.ToString());
   }
   fileName.Append(System.IO.Path.GetFileNameWithoutExtension(files[i].FileName));
   fileName.Append(DateTime.Now.ToString("yyMMddHHmmss"));
   fileName.Append(System.IO.Path.GetExtension(files[i].FileName));

   System.IO.Stream sm = files[i].InputStream;
   if (System.IO.File.Exists(@"D:\水印log.jpg"))
   {
   ImageHelper.ZoomAuto(sm, fileName.ToString(), 400, 300, "", @"D:\水印log.jpg");
   }
   else
   {
   ImageHelper.ZoomAuto(sm, fileName.ToString(), 400, 300, "水印LOG", "");
   }
   bool ok = System.IO.File.Exists(fileName.ToString());
   if (ok)
   {
   number++;
   }
  }
  if (number.Equals(files.Count))
  {
   check.Message = "上传成功！";
   check.Check = true;
  }
  else
  {
   check.Message = "失败！";
   check.Check = false;
  }
  return Json(check);
  }
  catch(Exception ex)
  {
  check.Message = ex.ToString();
  check.Check = false;
  return Json(check);
  }
 }

　/// <summary>
 /// 返回值
 /// </summary>
 public class Result<T>
 {
 public string Message { get; set; }
 public bool Check { get; set; }
 public IList<T> ResultList { get; set; }
 }

<system.web>
 <authentication mode="None" />
 <compilation debug="true" targetFramework="4.5" />
 <!--<httpRuntime targetFramework="4.5" />-->
 <httpRuntime executionTimeout="500" maxRequestLength="409600" useFullyQualifiedRedirectUrl="false" minFreeThreads="8" minLocalRequestFreeThreads="4" appRequestQueueLimit="100" />
 </system.web>