public void download()

{

    string fileName = "456.zip";//客户端保存的文件名

    string filePath = AppDomain.CurrentDomain.BaseDirectory.Replace("\\", "/") + "Excel/123.zip";

    System.IO.FileInfo fileInfo = new System.IO.FileInfo(filePath);

    if (fileInfo.Exists == true)

    {

        //每次读取文件，只读取1M，这样可以缓解服务器的压力

        const long ChunkSize = ;

        byte[] buffer = new byte[ChunkSize];

        Response.Clear();

        //获取文件

        System.IO.FileStream iStream = System.IO.File.OpenRead(filePath);

        //获取下载的文件总大小

        long dataLengthToRead = iStream.Length;

        //二进制流数据（如常见的文件下载）

        Response.ContentType = "application/octet-stream";

        //通知浏览器下载文件而不是打开

        Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName));

        //加上设置大小下载下来的.xlsx文件打开时才不会报“Excel 已完成文件级验证和修复。此工作簿的某些部分可能已被修复或丢弃”

        Response.AddHeader("Content-Length", iStream.Length.ToString());

        using (iStream)//解决文件占用问题，using 外 iStream.Dispose() 无法释放文件

        {

            while (dataLengthToRead >  && Response.IsClientConnected)

            {

                int lengthRead = iStream.Read(buffer, , Convert.ToInt32(ChunkSize));//读取的大小

                Response.OutputStream.Write(buffer, , lengthRead);

                Response.Flush();

                dataLengthToRead = dataLengthToRead - lengthRead;

            }

            iStream.Dispose();

            iStream.Close();

        }

        Response.Close();

        Response.End();

    }

}

Response.AddHeader("Content-Length", iStream.Length.ToString());