could use DrawItem event, to make it work, need set DrawMode property to OwnerDrawFixed.
private void comboBox1_DrawItem(object sender, DrawItemEventArgs e)
{
if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
{
lblSelectText.Text = this.comboBox1.Items[e.Index].ToString();
}
e.DrawBackground();
// draw text strings
e.Graphics.DrawString(
comboBox1.Items[e.Index].ToString(),
e.Font,
Brushes.Black, new Point(e.Bounds.X, e.Bounds.Y));
}