我这样写的:只能导出前二十条记录,不知道怎么回事.
 
HttpResponse resp;
        resp = Page.Response;
        resp.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");
        resp.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(FileName, System.Text.Encoding.UTF8).ToString() + ".xls");
        resp.ContentType = "application/ms-excel";
        string ls_title, ls_item;
        ls_title = string.Empty;
        ls_item = string.Empty;
        //定义表对象与行对像，同时用DataSet对其值进行初始化
        DataTable dt = ds.Tables[0];
        DataRow[] myRow = dt.Select("");
        ls_title += "排序\t 帐号\t 姓名\t 职位\t性质\n ";
        foreach (DataRow row in myRow)
        {
            ls_item += row["M_orderID"] + "\t" + row["M_userName"].ToString() + "\t" + row["M_realName"].ToString() + "\t" + Group.getGroupInfoById(row["M_department"].ToString(), "G_baseName") + "\t" + Group.getMemberTypeById(row["M_sign"].ToString(), "MT_typeName") + "\n";
        }
        resp.Write(ls_title + ls_item);
        //写缓冲区中的数据到HTTP头文件中
        resp.End();

你原来的那个DataGrid1,需要再建一个DataGrid2,按照下面的代码,没有问题,我就一直用着.
SqlConnection con=DB.createCon();
SqlDataAdapter sda=new SqlDataAdapter();
sda.SelectCommand=new SqlCommand("select * from person111",con);
DataSet ds=new DataSet();
sda.Fill(ds,"emp");
this.DataGrid2.DataSource=ds.Tables["emp"].DefaultView;
this.DataGrid2.DataBind();

Response.Clear();     
Response.Buffer=   true;     
Response.Charset="GB2312";           
Response.AppendHeader("Content-Disposition","attachment;filename=FileName.xls");     
Response.ContentEncoding=System.Text.Encoding.GetEncoding("GB2312");//设置输出流为简体中文   
Response.ContentType   =   "application/ms-excel";//设置输出文件类型为excel文件。     
this.EnableViewState   =   false;           
System.Globalization.CultureInfo   myCItrad   =   new   System.Globalization.CultureInfo("ZH-CN",true);   
   oStringWriter   =   new   (myCItrad);     
System.Web.UI.HtmlTextWriter   oHtmlTextWriter   =   new   System.Web.UI.HtmlTextWriter(oStringWriter);  
//导出DataGrid1中显示的数据
this.DataGrid2.RenderControl(oHtmlTextWriter);     
Response.Write(oStringWriter.ToString());   
Response.End();

我也是初学者,发了信息也是没有人给回,咱们都得求别人啊,求人不行,那就求自己吧.