Abstract: A kind of optical system with three-field of view for practical application was designed. The switch between wide and middle FOV was realized by using lenses group, and the switch between narrow and wide field was actualized by using mirrors. Three-field of view shared secondary imaging lens group, and the secondary imaging technique was used in the system design in order to endure 100% cold shield efficiency and reduce the diameter of the first lens. The technology for aspheric lenses was introduced to improve the imaging quality by correcting spherical aberration and coma. Then the performance of optical system was analyzed by CODE V software. The max spot was less than 11 m and MTF approached to diffraction limit. The results show that the image quality of optical system reaches application requirements. In addition, compact structure and light weight are the features of the system.