只需要把下列的代码Paste到按钮事件中即可：
        Response.Clear();
        Response.Buffer = true;
        Response.Charset = "GB2312";
        Response.AppendHeader("Content-Disposition", "attachment;filename=FileName.xls");
        // 如果设置为 GetEncoding("GB2312");导出的文件将会出现乱码！！！
        Response.ContentEncoding = System.Text.Encoding.UTF7;
        Response.ContentType = "application/ms-excel";//设置输出文件类型为excel文件。
        System.IO.StringWriter oStringWriter = new System.IO.StringWriter();
        System.Web.UI.HtmlTextWriter oHtmlTextWriter = new System.Web.UI.HtmlTextWriter(oStringWriter);
        this.GVIDVIEW的ID名称.RenderControl(oHtmlTextWriter);
        Response.Output.Write(oStringWriter.ToString());
        Response.Flush();
        Response.End();