public ActionResult UploadFile()
  {
   return View();
  }

  [HttpPost]
  public ActionResult UploadFile(HttpPostedFileBase file)
  {
   var fileName = file.FileName;
   var filePath = Server.MapPath(string.Format("~/{0}", "File"));
   file.SaveAs(Path.Combine(filePath, fileName));
   return View();
  }

<form action="/Home/UploadFile" method="post" enctype="multipart/form-data">
 <input type="file" name="file" /><br />
 <input type="submit" value="提交" />
</form>

 public class BlogModel
 {
  [Display(Name = "博客名称")]
  [Required(ErrorMessage = "请输入你的博客名称！")]
  public string BlogName { get; set; }

  [Display(Name = "博客地址")]
  [Required(ErrorMessage = "请输入你的博客地址！")]
  public string BlogAddress { get; set; }

  [Display(Name = "博客图片")]
  [Required(ErrorMessage = "请上传你的博客图片！")]
  [ValidateFile]
  public HttpPostedFileBase BlogPhoto { get; set; }
 }

 public class ValidateFileAttribute : ValidationAttribute
 {
  public override bool IsValid(object value)
  {
   int MaxContentLength = 1024 * 1024 * 4;
   string[] AllowedFileExtensions = new string[] { ".jpg", ".gif", ".png", ".pdf" };

   var file = value as HttpPostedFileBase;

   if (file == null)
    return false;
   else if (!AllowedFileExtensions.Contains(file.FileName.Substring(file.FileName.LastIndexOf('.'))))
   {
    ErrorMessage = "请上传你的博客图片类型: " + string.Join(", ", AllowedFileExtensions);
    return false;
   }
   else if (file.ContentLength > MaxContentLength)
   {
    ErrorMessage = "上传图片过大，不能超过4兆 : " + (MaxContentLength / 1024).ToString() + "MB";
    return false;
   }
   else
    return true;
  }
 }

  [HttpPost]
  public ActionResult UploadFile(BlogModel bModel)
  {
   if (ModelState.IsValid)
   {
    var fileName = bModel.BlogPhoto.FileName;
    var filePath = Server.MapPath(string.Format("~/{0}", "File"));
    bModel.BlogPhoto.SaveAs(Path.Combine(filePath, fileName));
    ModelState.Clear();
   }   
   return View();
  }

 <security>
  <requestFiltering>
  <requestLimits maxAllowedContentLength="2147483647">
  </requestLimits>
  </requestFiltering>
 </security>

<system.web>
 <httpRuntime maxRequestLength="2147483647" executionTimeout="100000" />
</system.web>

<system.webServer>
 <security>
 <requestFiltering>
  <requestLimits maxAllowedContentLength="2147483647" />
 </requestFiltering>
 </security>
</system.webServer>

<style type="text/css">
 .field-validation-error {
  color: red;
 }
</style>
<form id="uploadFileSub" action="/Home/UploadFile" method="post" enctype="multipart/form-data">
 <fieldset>
  <legend></legend>
  <ul class="lifile">
   <li>
    @Html.LabelFor(m => m.BlogName)<br />
    @Html.TextBoxFor(m => m.BlogName, new { maxlength = 50 })
    @Html.ValidationMessageFor(m => m.BlogName)
   </li>
   <li>
    @Html.LabelFor(m => m.BlogAddress)<br />
    @Html.TextBoxFor(m => m.BlogAddress, new { maxlength = 200 })
    @Html.ValidationMessageFor(m => m.BlogAddress)<br />
   </li>
   <li>
    @Html.LabelFor(m => m.BlogPhoto)
    @Html.TextBoxFor(m => m.BlogPhoto, new { type = "file" })
    @Html.ValidationMessageFor(m => m.BlogPhoto)
    <span id="warning" style="color:red;font-size:large;"></span>
   </li>
   <li>
    <input type="submit" value="提交" />
   </li>
  </ul>

 </fieldset>
</form>

 function GetFileSize(fileid) {
  var fileSize = 0;
  fileSize = $("#" + fileid)[0].files[0].size;
  fileSize = fileSize / 1048576;
  return fileSize;
 }

 function getNameFromPath(strFilepath) {
  var objRE = new RegExp(/([^\/\\]+)$/);
  var strName = objRE.exec(strFilepath);

  if (strName == null) {
   return null;
  }
  else {
   return strName[0];
  }
 }

  $("#BlogPhoto").change(function () {
   var file = getNameFromPath($(this).val());
   if (file != null) {
    var errors = $(document).find(".field-validation-error");
    $.each(errors, function (k, v) {
     if ($(v).attr("data-valmsg-for") === "BlogPhoto") {
      $(v).hide();
     }
    });
    var extension = file.substr((file.lastIndexOf('.') + 1));
    switch (extension) {
     case 'jpg':
     case 'png':
     case 'gif':
     case 'pdf':
      fileTypeBool = false;
      break;
     default:
      fileTypeBool = true;
    }
   }
   if (fileTypeBool) {
    $("#warning").html("只能上传扩展名为jpg,png,gif,pdf的文件！");
    return false;
   }
   else {
    var size = GetFileSize('BlogPhoto');
    if (size > 4) {
     fileSizeBool = true;
     $("#warning").html("上传文件已经超过4兆！");
    } else {
     fileSizeBool = false;
    }
   }
  });

  $("#uploadFileSub").submit(function () {
   $("input[type='text']").each(function (k, v) {
    if ($(v).length) {
     $(v).siblings("span").hide();
    }
   });
   if (fileTypeBool || fileSizeBool) {
    return false;
   }
  });

@using (Html.BeginForm("UploadFile", "Home", FormMethod.Post, new { enctype = "multipart/form-data" }))
{

 <input type="file" id="file" name="file" />
 <input type="submit" value="提交" />
}