int width = Screen.PrimaryScreen.Bounds.Width;

            int height = Screen.PrimaryScreen.Bounds.Height;

            Bitmap bmp = new Bitmap(width, height);

            using (Graphics g = Graphics.FromImage(bmp))
            {

                g.CopyFromScreen(0, 0, 0, 0, new Size(width, height));

            }
            bmp.Save(@"c:\1.jpg");
            bmp.Dispose();

参考：http://dotnet.chinaitlab.com/CSharp/794536.html