Based on the model of laser imaging radar detecting target, the trajectory forming process of target imaging points is analyzed, and the distribution function of echo peak points on the image surface under single pulse imaging. While the experiment is designed, a method of detecting target three-dimensional trajectory is put forward. The experimental image obtained by laser radar is processed through the adaptive thresholding algorithm, and the trajectory of target imaging points is got. Then the comparison between theoretical and experimental data is made, and the result shows that the relative error between trajectories detected by theoretical model and experiment is controlled in 2%, which has a better coincidence. The result can provide reference for the trajectory prediction and intention judge of aerial target.