添加 RowPostPaint 事件，事件代码如下：
private void dataGridView1_RowPostPaint(object sender, DataGridViewRowPostPaintEventArgs e)
{
Rectangle rectangle = new Rectangle(e.RowBounds.Location.X,
e.RowBounds.Location.Y,
this.dataGridView1.RowHeadersWidth - 4,
e.RowBounds.Height);
TextRenderer.DrawText(e.Graphics, (e.RowIndex + 1).ToString(),
this.dataGridView1.RowHeadersDefaultCellStyle.Font,
rectangle,
this.dataGridView1.RowHeadersDefaultCellStyle.ForeColor,
TextFormatFlags.VerticalCenter | TextFormatFlags.Right);
}