//服务器文件路径
string strFilePath = Server.MapPath("~") + "/excel/20170206104654.xlsx";
Fileinfo fileInfo = new FileInfo(strFilePath);
Response.Clear();
Response.AddHeader("content-disposITion", "attachment;filename=" + Server.UrlEncode(fileInfo.Name.ToString()));
Response.AddHeader("content-length", fileInfo.Length.ToString());
Response.ContentTyPE = "application/octet-stream";
Response.ContentEncoding = System.Text.Encoding.Default;
Response.WriteFile(strFilePath);