1.FileInfo objFileInfo = new FileInfo(Server.MapPath("~/DownloadFile.zip"));
2.Response.Clear();
3.Response.AddHeader("Content-Disposition", "attachment;filename=" + objFileInfo.Name);//Add File name to dialog display
4.Response.AddHeader("Content-Length", objFileInfo.Length.ToString());//Add the file length to dialog display
5.Response.ContentType = "application/octet-stream";
6.Response.WriteFile(objFileInfo.FullName);//download your file form service
7.Response.End();