Code
 HttpResponse resp = Page.Response;
                resp.Clear();
                resp.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");
                string head = "邮箱:" + "\t" + txtEmail.Text + "\t" + "数量:" + "\t" + Table.Rows.Count + "\t" + "邮件状态:" + "\t" + ddlStatus.SelectedValue + "\n";
                resp.Write(head);
                //resp.ContentEncoding = System.Text.Encoding.GetEncoding("UTF8");
                resp.ContentType = "application/ms-excel";
                
                //resp.AddHeader("Content-Disposition", "attachment; filename=" + System.Web.HttpUtility.UrlEncode(fileName.ToString(), System.Text.Encoding.UTF8) + ".xls");              
                resp.AddHeader("Content-Disposition", "attachment; filename=" +System.Web.HttpUtility.UrlEncode("邮件日志查询记录", System.Text.Encoding.UTF8)+".xls");
                this.EnableViewState = false;
                string colHeaders = "", Is_item = "";
                //定义表对象与行对象，同时使用DataSet对其值进行初始化
                DataRow[] myRow = Table.Select("");
                //取得数据表各列标题，标题之间以\t分割，最后一个列标题后加回车符
                //string[] arrTitle ={ "id", "主机", "发送日期", "发送时间", "邮件状态", "状态代码" };
                string[] arrTitle ={ "发送日期", "发送时间", "邮件状态", "状态代码" };
                for (int i = 0; i < Table.Columns.Count; i++)
                {
                    //colHeaders += Table.Columns[i].Caption.ToString() + "\t";
                    colHeaders += arrTitle[i] + "\t";
                }
                colHeaders += "\n";
                resp.Write(colHeaders);
                //逐行处理数据
                foreach (DataRow row in myRow)
                {
                    //在当前行中，逐列取得数据，数据之间以\t分割，结束时加回车符\n
                    for (int i = 0; i < Table.Columns.Count; i++)
                    {
                        Is_item += row[i].ToString() + "\t";
                    }
                    Is_item += "\n";
                    resp.Write(Is_item);
                    Is_item = "";
                }

Code
select cast(d.rundate as char(10)) as rundate,d.runtime,s.status,s.failcode from " + sendTable + " as d," + statusTable ……