Abstract: The power distribution of the echo wave is a key parameter for cateye detecting system and is usually affected by the aperture diffraction. The field distribution function of the cateye echo wave was derived according to the Collins formula and numerically calculated. The impacts of the caliber and focus length of imaging lens ,the detection distance, the beam waist and the defocusing amount on the power distribution of cat-eye echo wave were investigated. Moreover,a charge coupled device (CCD) based experimental system was set up to observe the power distribution of cateye echo wave and the diffraction pattern. The experiment results indicate that, the optic field of the echo wave carries obvious diffraction information;when the detector locates away from the focus plane of the imaging lens, within a limit detecting distance, the peak power of the cat-eye echo firstly increases and then decreases as the detecting distance increases, the maximum power emerges at about 100 cm. The observing result agrees well with the theoretical analysis,validating that the aperture diffraction can have a significant influence on the power distribution of echo wave. The investigation can provide an instruction for building a cat-eye based detecting system.