To reduce structural parameters needed in the process of the state space modeling of a fast steering mirror (FSM), a modeling method based on system identification is proposed. Only two structural parameters, namely, coil resistance and inductance, are needed when using this modeling method. Based on the state model, a set of combined control systems consisting of a reduced-order observer, state feedback, an internal model, and a stabilization compensator were designed; the internal model and stabilization compensator were designed by using state feedback. Furthermore, current and angular velocity can be obtained using a reduced-order observer. The combined system can progressively track of input signals and suppress disturbances; the simulation model was built using SIMULINK. The simulation results show that, compared with the incomplete differential proportional integral derivative (PID) control system, the setting time decreases by 53.6% and the overshoot increases by 131.2% without considering the disturbance in the composite system. The dynamic and steady-state performance of the incomplete differential PID control system decreases significantly after adding the disturbance signal, while the composite system is maintained. The simulation results verify the correctness of the theoretical analysis.