private void pictureBox1_MouseClick(object sender, MouseEventArgs e)
        {
            using (Graphics g = this.pictureBox1.CreateGraphics())
            {
                g.DrawLine(Pens.Red, e.X + 10, e.Y, e.X - 10, e.Y);
                g.DrawLine(Pens.Red, e.X, e.Y + 10, e.X, e.Y - 10);
            }
        }

------解决方案--------------------
private void pictureBox1_MouseClick(object sender, MouseEventArgs e)
       {
           using (Graphics g = this.pictureBox1.CreateGraphics())
           {
               g.DrawLine(Pens.Red, e.X + 10, e.Y, e.X - 10, e.Y);
               g.DrawLine(Pens.Red, e.X, e.Y + 10, e.X, e.Y - 10);
pictureBox1.Invalidate();
           }

       }