Based on optical design software ZEMAX and the Monte Carlo ray tracing method, a comparative study of three design methods of double-reflection focusing system under different angle aberrations are undertaken. And focusing performance parameters on the focusing plane are analyzed. The results show that any slight angle aberrations can lead to intense deterioration of the focusing performance and large deviation of the focusing location. When there is the angle aberration of the focusing system, different shapes of ignition areas appear for different design methods, which give rise to different flight trajectories and attitudes for the laser thrusters.