利用Tick事件

        bool moveLeft=false;

        private void Form1_Load(object sender, System.EventArgs e)
        {
            pictureBox1.Image=Image.FromFile(@"D:\u=2898196153,2623626892&gp=3.jpg");
            pictureBox1.Location=new Point(-this.Width,(this.Height-pictureBox1.Height)/2);
            timer1.Interval=10;
            timer1.Start();
        }

        private void timer1_Tick(object sender, System.EventArgs e)
        {
            if(moveLeft==false)
            {
                pictureBox1.Left +=10;
                if(pictureBox1.Left>this.Width)
                    moveLeft=true;
            }
            else
            {
                pictureBox1.Left -=10;
                if(pictureBox1.Left<(-pictureBox1.Width))
                    moveLeft=false;
            }
        }

太感谢楼上这位老师了