Bind the Data to the Gridview using SqlDatSource and one Button on the webpage.

How to Create a Excel sheet?
TextWriter
is used to Create a Excel Sheet by creting the StreamWriter class object.StreamWriter
class takes the path the of the excel sheet name as argument.Dont forget to use
the verbatile string (@) at the beginning of the path as follows:

TextWriter sw = new StreamWriter(@"F:\\ExcelData.xls");
 
The Extension of the Excel Sheet is .xls.It will automatically creats the excel
sheet with the name ExcelData in ‘F’Drive.If the Excel sheet is already
existing with the name ‘ExcelData’ it will overrides the Data. 

in .asp.cs page

using System;

using System.Data;

using System.Configuration;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

using System.Data.SqlClient;

using System.IO;

public partial class _Default : System.Web.UI.Page

{

    protected void Page_Load(object sender, EventArgs e)

    {

    }

//Double click your Button and write the below code to Export Gridview Data to Excel

    protected void Button1_Click(object sender, EventArgs e)

    {

    TextWriter sw = new StreamWriter(@"F:\\ExcelData.xls");

    //Getting the Gridview HeaderRow Values

sw.WriteLine(GridView1.HeaderRow.Cells[0].Text+"\t"+GridView1.HeaderRow.Cells[1].Text+"\t"

        +GridView1.HeaderRow.Cells[2].Text);

        for (int i = 0; i < GridView1.Rows.Count; i++)

        {

            //Getting the Gridview Row values

            sw.WriteLine(GridView1.Rows[i].Cells[0].Text  + "\t " + GridView1.Rows[i].Cells[1].Text  + "\t" + GridView1.Rows[i].Cells[2].Text );

        }

        sw.Close();//Don’t Forget to Close the StreamWrtier object.

    }

}

output of Excel sheet with data.

The Following Error occurs when you try to export a Data to Excel when the Excel Sheet is in open State.

Error Iamge.