最簡單的方法是在Datagridview的事件RowPostPaint事件下面添加如下代碼即可
 
 private void dataGridView1_RowPostPaint(object sender, DataGridViewRowPostPaintEventArgs e)
 
        {
            SolidBrush b = new SolidBrush(this.dataGridView1.RowHeadersDefaultCellStyle.ForeColor);
            e.Graphics.DrawString((e.RowIndex + 1).ToString(System.Globalization.CultureInfo.CurrentUICulture), this.dataGridView1.DefaultCellStyle.Font, b, e.RowBounds.Location.X + 20, e.RowBounds.Location.Y + 4);
 
 
        }

你可以重寫DataGridView的OnRowPostPaint方法或者直接在DataGridView的RowPostPaint事件裏寫，如下(重寫DataGridView的OnRowPostPaint方法)
using System;
using System.Text;
using System.Windows.Forms;
using System.Drawing;
namespace Test
{
    class DataGridViewEx : DataGridView
    {
        SolidBrush solidBrush;
        public DataGridViewEx()
        {
            solidBrush = new SolidBrush(this.RowHeadersDefaultCellStyle.ForeColor);
        }
        protected override void OnRowPostPaint(DataGridViewRowPostPaintEventArgs e)
        {
            e.Graphics.DrawString((e.RowIndex + 1).ToString(), e.InheritedRowStyle.Font, solidBrush, e.RowBounds.Location.X + 15, e.RowBounds.Location.Y + 5);
            base.OnRowPostPaint(e);
        }
    }
}

原文：https://www.cnblogs.com/xiaofengfeng/p/3422668.html

給datagridview 添加序號