public Form1()
        {
            InitializeComponent();
            pictureBox1.Paint += new PaintEventHandler(pictureBox_Paint);
            pictureBox2.Paint += new PaintEventHandler(pictureBox_Paint);
            pictureBox3.Paint += new PaintEventHandler(pictureBox_Paint);  
        }
        Image img = Image.FromFile(@"C:\Users\SaeWind\Desktop\123\1.png");
        void pictureBox_Paint(object sender, PaintEventArgs e)
        {
            PictureBox pic = (PictureBox)sender;
            Graphics g = e.Graphics;
            g.DrawImage(img, new Rectangle(0, 0, pic.Width, pic.Height));
        }

------解决方案--------------------
这样 pictureBox1.Image一直为null

------解决方案--------------------
新手，随便说下：能不能指向同一个栈区呢？