In the television-guided system, a short focal length lens with wide field of view is hoped when target recognition, however, a long focal length lens with narrow field of view is hoped when target tracking. The traditional method is to design a switch-zoom optical system, which is subject to losing target in the course of shifting, but a mechanical-compensated zoom lens can be a good balance between target acquisition and tracking. The principle of zoom lens and the optical parameters determination are described in the thesis, and a focal length from 20 to 100mm visible video zoom lens is designed, that field of view is 1.8°×1.38°~9°×6.8°. The results of experiments show the system has good image quality, and it not only can accurately track far spot target in the case of long focal length, but also can fast recognize and observe target in the case of short focal length.