Abstract: The detection range equation of cat-eye target was extended by modeling the detection process based on matrix optics, which can be applied to the situation that the cat-eye optical system had out-of-focus reflecting element and the detection beam was oblique incidence. The detection range equation was verified by field experiment. The results prove that there is small drift angle between the incidence beam and echo beam and the echo divergence angle is much larger than the echo drift angle, which makes the echo beam be large enough to cover the detection system. On conditions of the same detection parameters, the echo power is only related to the focal length and defocusing amount of the cat-eye optical system and has nothing to do with the incidence angel of detection beam and the receiving aperture of the cat-eye optical system.