Based on the research of space-based spatial object detectors,the optical environment of near-earth space was studied. Modeling of optical characteristics of small spatial object with shapes of plane,sphere,cylinder and cone was carried out,the dependence of the irradiance on objects at a certain distance to the azimuth angles,phase angles of light source and detectors were described. Under the same optical conditions,the brightest object for detector is plane,sphere and cylinder are darker,and cone is the darkest. To verify our modeling,experiments were carried out in dark room to simulate the optical detecting in space. Static and dynamic objects were captured by ICCD camera,by analyzing and processing the images,the correctness of the models and the feasibility of using low-light-imaging system to trace and survey the spatial objects were proved.