protected void btExcel_Click(object sender, EventArgs e)
    {
        DataSet ds = new DataSet();
        ds = Session["myDataSet"] as DataSet;
        DataTable DT = ds.Tables[0];
        //生成将要存放结果的Excel文件的名称
        string NewFileName = DateTime.Now.ToString("yyyyMMddHHmmss") + ".xls";
        //转换为物理路径
        NewFileName = Server.MapPath("~/Temp/" + NewFileName);
        //根据模板正式生成该Excel文件
        File.Copy(Server.MapPath("~/Temp/Module01.xls"), NewFileName, true);
        //建立指向该Excel文件的数据库连接
        string strConn = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + NewFileName + ";Extended Properties='Excel 8.0;'";
        OleDbConnection Conn = new OleDbConnection(strConn);
        //打开连接，为操作该文件做准备
        Conn.Open();
        OleDbCommand Cmd = new OleDbCommand("", Conn);

foreach (DataRow DR in DT.Rows)
        {
            string XSqlString = "insert into [Sheet1$]";
            XSqlString += "([举办年度],[名称],[主题],[举办时间],[举办地点],[承办单位],[预算],[实际规模],[评价]) values(";
            XSqlString += "'" + DR["Year"] + "',";
            XSqlString += "'" + DR["CampName"] + "',";
            XSqlString += "'" + DR["Topic"] + "',";
            XSqlString += "'" + DR["HeldTime"] + "',";
            XSqlString += "'" + DR["HeldPlace"] + "',";
            XSqlString += "'" + DR["UndertakeDep"] + "',";
            XSqlString += "'" + DR["Budget"] + "',";
            XSqlString += "'" + DR["ActualScale"] + "',";
            XSqlString += "'" + DR["Remarks"] + "')";
            Cmd.CommandText = XSqlString;
            Cmd.ExecuteNonQuery();
        }

//操作结束，关闭连接
        Conn.Close();
        //打开要下载的文件，并把该文件存放在FileStream中
        System.IO.FileStream Reader = System.IO.File.OpenRead(NewFileName);
        //文件传送的剩余字节数：初始值为文件的总大小
        long Length = Reader.Length;

Response.Buffer = false;
        Response.AddHeader("Connection", "Keep-Alive");
        Response.ContentType = "application/octet-stream";
        Response.AddHeader("Content-Disposition", "attachment; filename=" + Server.UrlEncode("夏令营信息.xls"));
        Response.AddHeader("Content-Length", Length.ToString());

byte[] Buffer = new Byte[10000];  //存放欲发送数据的缓冲区
        int ByteToRead;           //每次实际读取的字节数

while (Length > 0)
        {
            //剩余字节数不为零，继续传送
            if (Response.IsClientConnected)
            {
                //客户端浏览器还打开着，继续传送
                ByteToRead = Reader.Read(Buffer, 0, 10000);     //往缓冲区读入数据
                Response.OutputStream.Write(Buffer, 0, ByteToRead); //把缓冲区的数据写入客户端浏览器
                Response.Flush();                  //立即写入客户端
                Length -= ByteToRead;                //剩余字节数减少
            }
            else
            {
                //客户端浏览器已经断开，阻止继续循环
                Length = -1;
            }
        }

//关闭该文件
        Reader.Close();
        //删除该Excel文件
        File.Delete(NewFileName);
           }

方法2：

private void Export(GridView gvUser, string Style, string FileType, string FileName)
    {
        Response.ClearContent();
        Response.Charset = "GB2312";
        Response.ContentEncoding = System.Text.Encoding.UTF8;
        Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(FileName, System.Text.Encoding.UTF8).ToString());
        Response.ContentType = FileType;
        //page.Response.ContentType = "application/ms-excel";
        Page.EnableViewState = false;
        StringWriter sw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        //turn off paging
        gvUser.AllowPaging = false;
        BindGrid(gvUser);

gvUser.RenderControl(hw);
        Response.Write(Style);
        Response.Write(sw.ToString());
        //page.Response.Flush();
        Response.End();

//turn the paging on again
        gvUser.AllowPaging = true;
        BindGrid(gvUser);
    }
    private void BindGrid(GridView gvUser)
    {
        DataSet ds = new DataSet();
        ds = Session["myDataSet"] as DataSet;
        gvUser.DataSource = ds;
        gvUser.DataBind();
    }
    public override void VerifyRenderingInServerForm(Control control)
    {
    }
    protected void GridViewCamp_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        LinkButton deleteLB = (LinkButton)e.Row.FindControl("lbDelete");
        if (deleteLB != null)
        {
            deleteLB.Attributes.Add("onclick", "return confirm('您确实要删除所选择的数据项吗？');");
        }
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
          e.Row.Cells[0].Attributes["class"] = "text";
        }
    }

protected void btExcel_Click(object sender, EventArgs e)
    {

string strStyle = @"<style> .text { mso-number-format:\@; }</style>";
        //string strStyle = "";
        Export(GridViewCamp,strStyle,"application/ms-excel", "myExcel.xls");
    }

前台界面设置：EnableEventValidation="false"

<%@ Page Language="C#" AutoEventWireup="true" EnableEventValidation="false" CodeFile="CampInfo.aspx.cs" Inherits="Default3" %>