problem in displaying data in excel

Please change your PageLoad event code. No need for checking the IsPostBack condition on pageload.

Protected Sub Page_Load(sender As Object, e As System.EventArgs)
	GridView1.Visible = True
	GridView2.Visible = True
	Using con As New SqlConnection(constr)
		Using cmd As New SqlCommand("select dept as Department,count(*) Male_Count from per_det where gen='male' and regno1 in(select distinct regno17 from proof ) group by dept")
			Dim dacust1 As New SqlDataAdapter()
			cmd.Connection = con
			dacust1.SelectCommand = cmd
			Using dt As New DataTable()
				dacust1.Fill(dt)
				GridView1.DataSource = dt
				GridView1.DataBind()
			End Using
		End Using
	End Using
	Using con As New SqlConnection(constr)
		Using cmd As New SqlCommand("select dept AS Department,count(*) Female_Count  from per_det where gen='female' and regno1 in(select distinct regno17 from proof ) group by dept")
			Dim dacust1 As New SqlDataAdapter()
			cmd.Connection = con
			dacust1.SelectCommand = cmd
			Using dt As New DataTable()
				dacust1.Fill(dt)
				GridView2.DataSource = dt
				GridView2.DataBind()
			End Using
		End Using
	End Using
End Sub