<form enctype="multipart/form-data" method="post">
  <input type="file" id="file" />
  <input type="submit" value="上传" />
</form>

[HttpPost]
public ActionResult Upload(FormCollection form)
{
  if (Request.Files.Count == 0){
        //Request.Files.Count 文件数为0上传不成功
        return View();
      }
  var file = Request.Files[0];
  if (file.ContentLength == 0){
    //文件大小大（以字节为单位）为0时，做一些操作
    return View();
  }
  else{
    //文件大小不为0
    file = Request.Files[0]; //服务器上的UpLoadFile文件夹必须有读写权限
    string target = Server.MapPath("/")+("/Mock/Learning/");//取得目标文件夹的路径
    string filename = file.FileName;//取得文件名字
    string path = target + filename;//获取存储的目标地址
    file.SaveAs(path);}
    return View();
}

<system.web>
　　<httpRuntime maxRequestLength="40960"/> 
</system.web>

<form enctype="multipart/form-data" method="post">
  <div id="FileList">
    <div>
      <input type="file" id="file" name="file0"/>
    </div>
  </div>
  <p>
    <a onclick="AddFile();">添加文件</a>
  </p>
  <p>
    <input type="submit" value="上传" />
  </p>
</form>

<script>
var index = 1;    
function AddFile() {      
  var ul = document.getElementById("FileList");
  var inputDiv = document.createElement("div");
  inputDiv.setAttribute("Id", "div" + index);
  var file = document.createElement("input");
  file.setAttribute("type", "file");
  file.setAttribute("id", "file" + index);
  file.setAttribute("name", "file" + index);
  var btnDel = document.createElement("input");
  btnDel.setAttribute("type", "button");
  btnDel.setAttribute("value", "删除");
  btnDel.setAttribute("Id", index);
  btnDel.onclick = function() {
    inputDiv.removeChild(file);
    inputDiv.removeChild(btnDel);
    ul.removeChild(inputDiv);
  }      
  inputDiv.appendChild(file);
  inputDiv.appendChild(btnDel);
  ul.appendChild(inputDiv);
  index++;
}
</script>

[HttpPost]    
public ActionResult Upload(FormCollection form)    
{      
  foreach (string item in Request.Files)
  {        
    HttpPostedFileBase file = Request.Files[item] as HttpPostedFileBase;        
    if (file==null || file.ContentLength == 0)
      continue;  
    //判断Upload文件夹是否存在，不存在就创建
    string path = Server.MapPath("..//Upload"); 
    if (!System.IO.Directory.Exists(path)) 
    {          
      System.IO.Directory.CreateDirectory(path); 
    }       
    path = AppDomain.CurrentDomain.BaseDirectory + "Upload/";       
    //获取上传的文件名  
    string fileName = file.FileName; 
    //上传   
    file.SaveAs(Path.Combine(path,fileName)); 
  }      
  return Content("<script>alert('上传文件成功');window.history.back();</script>");   
}