A light optical system with wide bands, large field of view and lightweight was designed. The focal length is 35 mm, F-number is 7.5, working wavelength range is 400-900 nm, and a view angle is 60°. A complex double-Gauss construction was applied in the designed system, and spherical surfaces were used in all lens, so that the total length could be 115 mm and minimum modulation transfer function could be greater than 0.45 at 70 lp/mm. Barrel distortion and aberration vignetting were used to improve illuminance distribution homogeneity, marking the margin field illuminance reach 80% and the image plane illumination uniformity be 8%. This optical system has a good thermo-optical properties, can achieve fine image quality at the working temperature range of 0-40 Celsius, which is suitable for the deep space exploration.