Abstract: Design of detection system for cat-eye effect echo is mainly based on the energy properties of retro-reflection beam passing through optical window. The energy model of retro-reflection beam is set up by using the Collins formula in this research. The beam energy properties, including the spatial propagation, spatial distribution and echo energy received by detection system, were given by numerical computation. Experiments were implemented to verify the effectiveness of the model. The results show that the energy property of the retro-reflection beam is decided by the factors, such as focal length, aperture size, defocusing amount of the optical system and the incidence angle, which can not be analyzed with geometrical optics method. The echo beam center of figure will drift from the laser emission point when the incidence angle is increased. Experiments also show that, when the incidence angel changes within the range of field of view, the spatial distribution of the retro-reflection beam has little variation.