I have solved it.:)
on page load using this code.
protected void Page_Load(object sender, EventArgs e)
{
SqlCommand SelectCommand = new SqlCommand("select Id,Title,owner from PostAd1 where owner=@owner",conn);
SelectCommand.Parameters.Add("@owner", SqlDbType.NVarChar);
SelectCommand.Parameters[0].Value = Convert.ToString(Session["username"].ToString());
SqlDataAdapter da = new SqlDataAdapter(SelectCommand);
da.Fill(ds);
Gridview1.DataSource = ds;
Gridview1.DataBind();
}
[edit]code block added[/edit]