Risley prisms in laser 3D imaging radar can effectively reduce the size and weight of the system, which have the advantages of low energy consumption, high precision, and vibration insensitivity. However, the scanning trajectory is complicated, and there is a large amount of redundancy in the scanning points. Firstly, the distribution law of scanning trajectories was studied based on the first-order approximation formula. The variation characteristics of the distance between the scanning trajectories and the distance between the discrete scanning points were then analyzed. Finally, the system scanning parameters for full field of view coverage were obtained. The results show that when full field of view is covered, the counter-rotation and co-rotation have the same system scanning parameters and both have the same minimum redundancy 2π and identical scanning parameters except for the direction of rotation. When the effective scanning field of view and resolution are fixed, at specific speed pair, the partial coverage of the counter-rotation can reduce 1/4 of the redundancy and half-period co-rotation can reduce half of the redundancy. The reduction of redundancy means that the imaging frame rate is increased.