string filePath = Server.MapPath("~/yourCatalog/yourFile.xxx");
        FileStream fs = new FileStream(filePath, FileMode.Open);
        byte[] bytes = new byte[(int)fs.Length];
        fs.Read(bytes, 0, bytes.Length);
        fs.Close();
        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("yourFile.xxx", System.Text.Encoding.UTF8));
        Response.BinaryWrite(bytes);
        Response.Flush();
        Response.End();