Range-gated lidar imaging has dislocation distortion in dynamic environment. An assessment criterion is introduced for lidar image with Zernike moment invariants. Zernike moment invariant standard deviations of images under different imaging frame frequencies are calculated in dynamic imaging. The image distortion can be effectively indicated by the relative change of various moment invariant standard deviations. Laser imaging radar is simulated by Vega simulation platform and emulation image of range-gated imaging is obtained. Experiment image is obtained by imaging system and vehicular platform, which are built in our laboratory. Both experiment and simulation results show that if the imaging frequency is larger than 5 Hz the composite image has no distortion, and the image distortion can be evaluated effectively with Zernike moment invariants.