其实这个程序完全重画也不会很慢的，我给你改了下：
C# code
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Threading;

namespace Paint
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        int x1=10;
        int max = 600;
        public  void GrahpicsUpdate(Graphics graphics)
        {
            Pen mypen = new Pen(Color.Black);
            Pen mypen1 = new Pen(Color.Red);
            System.Drawing.Font font = new System.Drawing.Font("Arial", 8, FontStyle.Regular);
            graphics.DrawLine(mypen, 0, 192, 700, 192);
            String[] n = { "0%", "10%", "20%", "30%", "40%", "50%", "60%", "70%", "80%", "90%", "100%" };
            int xstart = 10;
            for (int i = 0; i < 11; i++)
            {
                graphics.DrawString(n[i].ToString(), font, Brushes.DarkGray, xstart - 7, 192);//.Red
                int Xmin = xstart;
                for (int j = 0; j < 9; j++)
                {
                    Xmin += 6;
                    if (j == 4) graphics.DrawLine(mypen, Xmin, 184, Xmin, 192);
                    else graphics.DrawLine(mypen, Xmin, 188, Xmin, 192);
                }
                graphics.DrawLine(mypen, xstart, 182, xstart, 192);
                xstart = xstart + 60;
            }
            graphics.DrawLine(mypen1, x1, 180, x1, 200);
        }

        private void groupBox2_Paint(object sender, PaintEventArgs e)
        {
            GrahpicsUpdate(e.Graphics);
        }

        private void textBox5_TextChanged(object sender, EventArgs e)
        {
            double d = Convert.ToDouble(textBoxPresentVal.Text);
            x1 = (int)(d / 100 * max)+10;
            groupBox1.Invalidate(); //这里可以传入要更新的区域，不过我觉得没有必要，反而破坏了算法的简洁性，如果不是刻意地追求效率
        }
    }
}