Abstract: The way and characteristics of space debris detection was analyzed. Based on the discussion of the requirements of space-based optical detection system, the system's technical specifications were presented. The detection of brightness higher than sixth-magnitude stars target was achieved, the target positioning precision could reach 3.5. Through the analysis, the influence of stray light which produced of the strong light source in the field of view was controlled in the design process, and the performance of the bright and dark objects could be observed simultaneously. Technical specifications of optical system were:82 mm effective focal length; 70 mm pupil diameter; 1010 field of view; under the condition of 450-900 nm wavelength range, 2 600-9 800 K color temperature range, the deviation of energy centre is better than 3m in the field of view of 0.85, the deviation of energy centre between the various temperature color is better than 1m, meanwhile, spot diagram energy concentration is greater than 75% in the 22 pixel and the spot diagram energy concentration is not less than 90% in the 33 pixel. The requirements of dark targets observation can be met by the sun to suppress the angle is greater than 50, and the PST is not higher than 10-8 which are indicated by the simulation and analysis with the design of baffles and camera lens structures.