程序代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing;
using System.Diagnostics;

namespace Winform中DataGridView单元格内容字体突出显示
{
    class MyDataGridView : DataGridView
    {

        public MyDataGridView()
        {

        }
        public Color KeyColor { get; set; }
        public string KeyWord { get; set; }

        protected override void OnCellPainting(DataGridViewCellPaintingEventArgs e)
        {
            base.OnCellPainting(e);

            if (e.Value != null)
            {
                string cellValue = e.Value.ToString();//单元格原本内容
                Rectangle cellRect = e.CellBounds;//默认单元格
                float fontSizeWidth = 96 / (72 / e.CellStyle.Font.Size);
                float fontSizeHeight = 96 / (72 / e.CellStyle.Font.Size);
                //用一个list来保存关键字及对应的区域
                List<KeyValuePair<string, Rectangle>> cc = new List<KeyValuePair<string, Rectangle>>();

                //分解关键字;隔开的
                string[] al = this.KeyWord.Split(';');
                foreach (string i in al)
                {
                    if (cellValue.Contains(i))
                    {
                        Rectangle ee = e.CellBounds;  //单元格内容区域，默认定义为单元格大小
                        //关键字的坐标
                        ee.X += cellValue.Substring(0, cellValue.IndexOf(i)).Length * (int)fontSizeWidth; //关键字左下角点坐标
                        ee.Y += (e.CellBounds.Height - (int)fontSizeHeight) / 2;//关键字右上角点坐标
                        cc.Add(new KeyValuePair<string, Rectangle>(i, ee));//收集到所有关键字的区域
                    }
                }
                if (cc.Count > 0)
                {
                    //原文本的Y坐标
                    cellRect.Y = cc[0].Value.Y;//这一句有bug,对自动换行的有问题

                    //绘制背景色
                    e.PaintBackground(e.ClipBounds, false);

                    //绘制背景色(被选中状态下)
                    if (e.State == (DataGridViewElementStates.Displayed | DataGridViewElementStates.Selected | DataGridViewElementStates.Visible))
                    {
                        e.PaintBackground(e.ClipBounds, true);
                    }

                    //分别绘制原文本和现在改变颜色的文本
                    e.Graphics.DrawString(cellValue, this.Font, new SolidBrush(e.CellStyle.ForeColor), cellRect, StringFormat.GenericDefault);

                    cc.ForEach(p =>
                    {
                        e.Graphics.DrawString(p.Key, this.Font, new SolidBrush(this.KeyColor), p.Value, StringFormat.GenericDefault);
                    });

                    //提交事务
                    e.Handled = true;
                }

            }

        }
    }
}