▲ 效果

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace DrawEx
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.StartPosition = FormStartPosition.CenterScreen;
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            string[] month = new string[] { "一月", "二月", "三月", "四月", "五月", "六月", "七月", "八月", "九月", "十月", "十一月", "十二月" };
            float[] data = new float[] { 20.5F, 60, 10.8F, 15.6F, 30, 110.9F, 96.3F, 30.7F, 70, 50.4F, 30.8F, 20 };

            Bitmap bMap = new Bitmap(500, 500);
            Graphics gph = Graphics.FromImage(bMap);
            gph.Clear(Color.Gray);
            PointF cPt = new PointF(40, 460);
            PointF xAxisEndPoint = new PointF(cPt.X + 420, cPt.Y);
            PointF yAxisEndPoint = new PointF(cPt.X, cPt.Y - 420);
            PointF[] xPt = new PointF[3] { new PointF(xAxisEndPoint.X + 15, xAxisEndPoint.Y), new PointF(xAxisEndPoint.X, xAxisEndPoint.Y - 5), new PointF(xAxisEndPoint.X, xAxisEndPoint.Y + 5) };
            PointF[] yPt = new PointF[3] { new PointF(yAxisEndPoint.X, yAxisEndPoint.Y - 15), new PointF(yAxisEndPoint.X - 3, yAxisEndPoint.Y), new PointF(yAxisEndPoint.X + 3, yAxisEndPoint.Y) };

            gph.DrawString("绘制折线图练习", new Font("宋体", 14), Brushes.Black, new PointF(cPt.X + 150, cPt.Y - 450));
            gph.DrawLine(Pens.Black, cPt.X, cPt.Y, cPt.X + 420, cPt.Y);
            gph.DrawLine(Pens.Black, cPt, new PointF(cPt.X, cPt.Y - 420));
            gph.DrawPolygon(Pens.Black, xPt); // 画轴三角形
            gph.FillPolygon(new SolidBrush(Color.Black), xPt);
            gph.DrawPolygon(Pens.Black, yPt); // 画轴三角形
            gph.FillPolygon(new SolidBrush(Color.Black), yPt);

            gph.DrawString("单位(万)", new Font("宋体", 12), Brushes.Black, new PointF(yPt[0].X - 26, yPt[0].Y - 18));
            gph.DrawString("月份", new Font("宋体", 12), Brushes.Black, new PointF(xPt[0].X - 26, xPt[0].Y + 18));

            PointF point1;
            PointF point2 = cPt;

            for (int i = 1; i <= month.Length; i++) {
                // 画Y轴刻度和标签
                gph.DrawLine(Pens.Black, cPt.X, cPt.Y - i * 35, cPt.X - 5, cPt.Y - i * 35);
                gph.DrawString((i * 10).ToString(), new Font("宋体", 12), Brushes.Black, new PointF(cPt.X - 30, cPt.Y - i * 35 - 6));
                // 画X轴的刻度和标签
                gph.DrawLine(Pens.Black, cPt.X + i * 32, cPt.Y, cPt.X + i * 32, cPt.Y + 5);
                if (i < 11)
                    gph.DrawString(month[i - 1].ToString(), new Font("宋体", 10), Brushes.Black, new PointF(cPt.X + 32 * i - 20, cPt.Y + 15));
                else
                    gph.DrawString(month[i - 1].ToString(), new Font("宋体", 8), Brushes.Black, new PointF(cPt.X + 32 * i - 12, cPt.Y + 15));

                point1 = new PointF(cPt.X + i * 32, cPt.Y - data[i - 1] * 3.5f);
                // 画折线
                if (i > 1) {
                    gph.DrawLine(Pens.Red, point1, point2);
                }
                //画没点的数值标签
                gph.DrawString(data[i - 1].ToString(), new Font("宋体", 11), Brushes.Blue, new PointF(point1.X + 1, point1.Y + 3));
                // 数值原点
                gph.FillEllipse(new SolidBrush(Color.Black), point1.X, point1.Y, 5, 5);
                point2 = point1;
            }

            pictureBox1.Image = bMap;
        }
    }
}

pictureBox1的Anchor属性设置了：Top，Bottom，Left，Right。整体思路是，先画在一个图片上面，然后再把图片加载到pictureBox1里面去，这样不会动下窗口就消失。

主要用了Graphics类里面的DrawString，DrawLine，DrawPolygon，FillPolygon等函数。

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参考：
《C#入门到精通》