public class PictureController : Controller
  {
    private IHostingEnvironment hostingEnv;

    public PictureController(IHostingEnvironment env)
    {
      this.hostingEnv = env;
    }
    // GET: /<controller>/
    public IActionResult Index()
    {
      return View();
    }
    public IActionResult UploadFiles()
    {
      return View();
    }
    [HttpPost]
    public IActionResult UploadFiles(IList<IFormFile> files)
    {
      long size = 0;
      foreach (var file in files)
      {
        var filename = ContentDispositionHeaderValue
                .Parse(file.ContentDisposition)
                .FileName
                .Trim('"');
        //这个hostingEnv.WebRootPath就是要存的地址可以改下
        filename = hostingEnv.WebRootPath + $@"\{filename}";
        size += file.Length;
        using (FileStream fs = System.IO.File.Create(filename))
        {
          file.CopyTo(fs);
          fs.Flush();
        }
      }
      ViewBag.Message = $"{files.Count} file(s) /{ size}bytes uploaded successfully!";
       return View();
    }

  }

<form asp-action="UploadFiles"
         asp-controller="Picture"
         method="post"
         enctype="multipart/form-data">
        <input type="file" name="files" multiple />
        <input type="submit" value="Upload Selected Files" />
 </form>

    public IActionResult UploadFilesAjax()
    {
      return View();
    }
    [HttpPost]
    public IActionResult UploadFilesAjax(string z) 
    {
      long size = 0;
      var files = Request.Form.Files;
      foreach (var file in files)
      {
        var filename = ContentDispositionHeaderValue
                .Parse(file.ContentDisposition)
                .FileName
                .Trim('"');
        filename = @"C:\Users\lg.HL\Desktop" + $@"\{filename}";    
        size += file.Length;
        using (FileStream fs = System.IO.File.Create(filename))
        {
          file.CopyTo(fs);
          fs.Flush();
        }
      }
      string message = $"{files.Count} file(s) / { size}bytes uploaded successfully!";
        return Json(message);
    }

<form method="post" enctype="multipart/form-data">
      <input type="file" id="files"
          name="files" multiple />
      <input type="button"
          id="upload"
          value="Upload Selected Files" />
 </form>

<script type="text/javascript">
    $(document).ready(function () {
      $("#upload").click(function (evt) {
        var fileUpload = $("#files").get(0);
        var files = fileUpload.files;
        var data = new FormData();
        for (var i = 0; i < files.length ; i++) {
          data.append(files[i].name, files[i]);
        }
        $.ajax({
          type: "POST",
          url: "/Picture/UploadFilesAjax",
          contentType: false,
          processData: false,
          data: data,
          success: function (message) {
            alert(message);
          },
          error: function () {
            alert("There was error uploading files!");
          }
        });
      });
    });
</script>