Relation knowledge of physical optics, Collins diffraction integral formula and the complex Gaussies function decomposition method of hard edge aperture are used to deduce the temporal distribution expressions of the reflection light of the coherent base mode Gaussian beam passing through the Cassegrain lens at back point. Influences of the fringe spacing and center shade ratio on the temporal distribution of the reflection light of Cassegrain lens are analyzed by numerical simulation. Experiments are designed and numerical results are verified. Results show that when the fringe spacing increases, peak number and peak intensity of the reflection light temporal distribution of Cassegrain lens reduce, and the frequency component of the echo envelope decreases. The increase of the center shade ratio leads to the loss of the energy and frequency components of the reflection light temporal distribution. With the increase of scanning speed, the distribution of echo signal becomes dense, and shows the trend of decreasing variance and increasing skewness and kurtosis. Kurtosis characteristics of the echo signal of Cassegrain lens and transmission lens are numerically different, and the two lens targets can be distinguished by the statistical characteristics of the echo signal. Results are meaningful to the application of laser active interferometric detection and recognition technology.