A fast mirror (FSM) system based on position sensitive detector (PSD) is introduced. The mechanical structure of the system is analyzed and designed. Incomplete differential proportional-integral-differential (PID) algorithm is used as a control strategy to remove the mechanical resonant peak with low frequency from FSM system. So the functions of fast response and wide bandwidth control of the FSM are realized. The corrected system has the characteristics of short step response time and high tracking precision through simulation verification.