Related answers to questions about how to download multiple files at the same time in asp.net

 ckl_ck.Items.Clear();
 DirectoryInfo TheFolder = new DirectoryInfo(Server.MapPath("Resource/Help"));
 //遍历文件夹下的文件
 foreach (FileInfo NextFile in TheFolder.GetFiles())
  this.ckl_ck.Items.Add(NextFile.Name);

 protected void Btn_down_Click(object sender, EventArgs e)
 {
 if (ckl_ck.Items.Count > 0)
 {
  List<string> listFJ = new List<string>();//保存附件路径
  List<string> listFJName = new List<string>();//保存附件名字
  for (int i = 0; i < ckl_ck.Items.Count; i++)
  {
  if (ckl_ck.Items[i].Selected)
  {
   listFJ.Add(Server.MapPath("Resource/Help/") + ckl_ck.Items[i].Text);
   listFJName.Add(ckl_ck.Items[i].Text);
  }

  }
  string time = DateTime.Now.Ticks.ToString();
  ZipFileMain(listFJ.ToArray(), listFJName.ToArray(), Server.MapPath("Resource/Help/" + time + ".zip"), 9);//压缩文件
  DownloadFile(Server.UrlEncode("附件.zip"), Server.MapPath("Resource/Help/" + time + ".zip"));//下载文件
 }
 }
 private void DownloadFile(string fileName, string filePath)
 {
 FileInfo fileInfo = new FileInfo(filePath);
 Response.Clear();
 Response.ClearContent();
 Response.ClearHeaders();
 Response.AddHeader("Content-Disposition", "attachment;filename=" + fileName);
 Response.AddHeader("Content-Length", fileInfo.Length.ToString());
 Response.AddHeader("Content-Transfer-Encoding", "binary");
 Response.ContentType = "application/octet-stream";
 Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");
 Response.WriteFile(fileInfo.FullName);
 Response.Flush();
 File.Delete(filePath);//删除已下载文件
 Response.End();
 }

 /// <summary>
 /// 压缩文件
 /// </summary>
 /// <param name="fileName">要压缩的所有文件（完全路径)</param>
 /// <param name="fileName">文件名称</param>
 /// <param name="name">压缩后文件路径</param>
 /// <param name="Level">压缩级别</param>
 public void ZipFileMain(string[] filenames, string[] fileName, string name, int Level)
 {
 ZipOutputStream s = new ZipOutputStream(File.Create(name));
 Crc32 crc = new Crc32();
 //压缩级别
 s.SetLevel(Level); // 0 - store only to 9 - means best compression
 try
 {
  int m = 0;
  foreach (string file in filenames)
  {
  //打开压缩文件
  FileStream fs = File.OpenRead(file);//文件地址
  byte[] buffer = new byte[fs.Length];
  fs.Read(buffer, 0, buffer.Length);
  //建立压缩实体
  ZipEntry entry = new ZipEntry(fileName[m].ToString());//原文件名
  //时间
  entry.DateTime = DateTime.Now;
  //空间大小
  entry.Size = fs.Length;
  fs.Close();
  crc.Reset();
  crc.Update(buffer);
  entry.Crc = crc.Value;
  s.PutNextEntry(entry);
  s.Write(buffer, 0, buffer.Length);
  m++;
  }
 }
 catch
 {
  throw;
 }
 finally
 {
  s.Finish();
  s.Close();
 }
 }