Abstract: According to the analysis of the working principle of laser semi-active proportional seeker, the characteristics of the optical system were summarized. Based on the overall design requests, an optical system of laser semi-active proportional seeker,with 1.064 m waveband,38 mm focal length,3 instantaneous field of view (IFOV) and 1 linear zone, was designed. The wavefront with large lateral spherical aberrations was simulated by Zernike polynomial and superposed on the incident wave surface, then the system was optimized.By changing the lateral spherical aberrations ,the size and uniformity of image facula could be regulated, and the diameter of facula was determined as 1.5 mm.