if (!ModelState.IsValid)
         {
            List<string> sb = new
       List<string>();
              //获取所有错误的Key  
            List<string> Keys = ModelState.Keys.ToList();
              //获取每一个key对应的ModelStateDictionary  
                foreach (var key in Keys)
                {
                   var errors = ModelState[key].Errors.ToList();
                  //将错误描述添加到sb中  
                    foreach (var error in errors)
                  {
                       sb.Add(error.ErrorMessage);
                }
             }
               return Json(sb);
           }  

C# 错误捕捉