A reduced-order autodisturbance rejection control method was proposed to improve the control performance of a fast steering mirror(FSM) driven by VCA applied in aerial photoelectric loads. The FSM model was analyzed, and the model parameters were obtained. Based on the theory of active disturbance rejection control (ADRC), the general third-order ADRC of the FSM was designed. The eddy current sensor measurement results were assumed, and the reduced-order extended state observer and its corresponding ADRC design method were proposed. Based on the controller bandwidth design theory, the control law of the second-order under damped object, such as FSM, was deduced, and the specific realization form of the control law with the disturbance compensation value was provided. The experimental results show that the reduced-order ADRC can significantly improve the dynamic performance of the positional step response of the FSM and can achieve a step response without overshoot and oscillation. The steady-state time reduces from 11.7 to 9.2 ms.In addition, the tracking steady-state error of the position ramp response declines, and the dynamic process of speed response improved. The speed stabilization time of image motion compensation drops from 10.2 to 7.8 ms, which is approximately 24%. The reduced-order ADRC can significantly improve the dynamic performance of FSM because of its simpler implementation and less computation.