The echo-wave was deduced based on the Huygens-Fresnel diffraction formula. The numerical results with the two-dimensional grating as focal plane device of staring photoelectric imaging system were verified experimentally. The impact of aperture size on the correlation between the echo image and the modulation of focal plane device was analyzed, and the influence of the cut-off frequency on the echo-wave was also discussed. With the size of aperture decreasing, the information of echo wave decreases, and the correlation also decreases. What′s more, with the aperture size increasing, more and more diffraction spots from the grating appear in the echo-wave image which shows complex pattern because of the interference between the spots. The spatial frequency of the pattern reflects the overlapping of the diffraction spot. The study of echo characteristics has practical application value for laser active detection on photoelectric reconnaissance equipment.