Hi ramco1917,

Note: For this sample i have used below article. For more details refer below article link.

Group GridView Header Row Columns by merging Cells in ASP.Net

Please refer below sample.

HTML

<asp:GridView ID="gvStudents" runat="server" AutoGenerateColumns="false" OnDataBound="OnDataBound">
    <Columns>
        <asp:BoundField DataField="ID" HeaderText="ID" />
        <asp:BoundField DataField="Pass" HeaderText="Pass" />
        <asp:BoundField DataField="Fail" HeaderText="Fail" />
    </Columns>
</asp:GridView>

Namespaces

C#

using System.Data;
using System.Drawing;

VB.Net

Imports System.Data
Imports System.Drawing

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt1 = new DataTable();
        dt1.Columns.AddRange(new DataColumn[] { new DataColumn("ID"),
                                                new DataColumn("Marks")});
        dt1.Rows.Add("1", "P");
        dt1.Rows.Add("2", "F");
        dt1.Rows.Add("3", "P");

        DataTable dt2 = new DataTable();
        dt2.Columns.AddRange(new DataColumn[] { new DataColumn("ID"),
                                                new DataColumn("Pass"),
                                                new DataColumn("Fail")});
        for (int i = 0; i < dt1.Rows.Count; i++)
        {
            DataRow dr = dt2.NewRow();
            dr["ID"] = dt1.Rows[i]["ID"];
            dr["Pass"] = Convert.ToString(dt1.Rows[i]["Marks"]) == "P" ? "P" : "";
            dr["Fail"] = Convert.ToString(dt1.Rows[i]["Marks"]) == "F" ? "F" : "";
            dt2.Rows.Add(dr);
        }
        gvStudents.DataSource = dt2;
        gvStudents.DataBind();
        gvStudents.HeaderRow.Cells[0].Text = "";
    }
}

protected void OnDataBound(object sender, EventArgs e)
{
    GridViewRow row = new GridViewRow(0, 0, DataControlRowType.Header, DataControlRowState.Normal);
    TableHeaderCell cell = new TableHeaderCell();
    cell.Text = "ID";
    cell.ColumnSpan = 1;
    row.Controls.Add(cell);

    cell = new TableHeaderCell();
    cell.ColumnSpan = 2;
    cell.Text = "Result";
    row.Controls.Add(cell);
    gvStudents.HeaderRow.Parent.Controls.AddAt(0, row);
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim dt1 As DataTable = New DataTable()
        dt1.Columns.AddRange(New DataColumn() {
                             New DataColumn("ID"),
                             New DataColumn("Marks")})
        dt1.Rows.Add("1", "P")
        dt1.Rows.Add("2", "F")
        dt1.Rows.Add("3", "P")
        Dim dt2 As DataTable = New DataTable()
        dt2.Columns.AddRange(New DataColumn() {
                             New DataColumn("ID"),
                             New DataColumn("Pass"),
                             New DataColumn("Fail")})
        For i As Integer = 0 To dt1.Rows.Count - 1
            Dim dr As DataRow = dt2.NewRow()
            dr("ID") = dt1.Rows(i)("ID")
            dr("Pass") = If(Convert.ToString(dt1.Rows(i)("Marks")) = "P", "P", "")
            dr("Fail") = If(Convert.ToString(dt1.Rows(i)("Marks")) = "F", "F", "")
            dt2.Rows.Add(dr)
        Next
        gvStudents.DataSource = dt2
        gvStudents.DataBind()
        gvStudents.HeaderRow.Cells(0).Text = ""
    End If
End Sub

Protected Sub OnDataBound(ByVal sender As Object, ByVal e As EventArgs)
    Dim row As GridViewRow = New GridViewRow(0, 0, DataControlRowType.Header, DataControlRowState.Normal)
    Dim cell As TableHeaderCell = New TableHeaderCell()
    cell.Text = "ID"
    cell.ColumnSpan = 1
    row.Controls.Add(cell)
    cell = New TableHeaderCell()
    cell.ColumnSpan = 2
    cell.Text = "Result"
    row.Controls.Add(cell)
    gvStudents.HeaderRow.Parent.Controls.AddAt(0, row)
End Sub

Screenshot