public static string ExportCSV(DataSet ds)
        {
            string data = "";
            foreach (DataTable tb in ds.Tables)
            {
                //写出列名
                foreach (DataColumn column in tb.Columns)
                {
                    data += column.ColumnName + ",";
                }
                data += "\n";
                //写出数据
                foreach (DataRow row in tb.Rows)
                {
                    foreach (DataColumn column in tb.Columns)
                    {
                        data += row[column].ToString() + ",";
                    }
                    data += "\n";
                }
                data += "\n";
            } return data;
        }

                string data = Export.ExportCSV(ds);
                Response.Clear();
                Response.Buffer = true;
                Response.Charset = "GB2312";
                Response.AppendHeader("Content-Disposition", "attachment;filename=数据导出.csv");
                Response.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");//设置输出流为简体中文
                Response.ContentType = "application/csv";
                Response.Write(data);
                Response.End();