Abstract: In order to study effect of incident angles on echo intensity distribution of a cat's eye photoelectric system, the model of intensity distribution of Gaussian beam passing through the cat's eye photoelectric system was built on the basis of generalized diffraction integral formula and the analytical expressions of transmission were deduced. The intensity distribution varying with the incident angle at two detection distances was simulated numerically. The results show that in the range of half the field of view of a cat's eye photoelectric system, when incident beam is Gaussian beam, the power of echo light beam becomes smaller with the increase of detection distance and incident angle and the distribution mode is close to Gaussian mode. Compared with the short distance detection, echo intensity distribution of the long distance detection which reaches the Gaussian mode has more stringent demands for incidence condition. This study provides theoretical basis for actual detection and has particular significance for selection of incidence angles.