Abstract: A large diameter and megapixels zoom optical imaging lens with CCD image sensor for monitoring system was designed, with the size of CCD at 1/3 inches, and the size of the pixel at 3.75 m. F numbers of lens in the position of short-focus, medium-focus, and long-focus were 1.6, 2.1, and 2.4 respectively. The zoom system was made up of four components, comparing to the traditional zoom system, the 4th component was adopted as compensation group in the zoom system. The initial structure was obtained by using the Gaussian method, the system was optimized by using Zemax software, and it was made up of the spherical lens. The lens field of view on the axis was greater than 0.3 at 133 lp/mm, off-axis 0.7 field of view was greater than 0.2 at 133 lp/mm. Minimum back intercept range of the system was greater than 9 mm, which met the assembly requirements. Finally, the zoom cam curve was mapped out by the method of multi-point fitting.