The influence of the uncertain disturbance from a variational aircraft attitude angular velocity on the forward image motion compensation of reflector in an aerial camera was researched and a disturbance observer was designed to observe the equivalent disturbance restrained by the corresponding compensation of the controller. The mathematic model for a mirror system was introduced based on the torque disturbance. Then, the external torque disturbance and the difference between nominal model and actual target caused by the variational model parameters were equivalent to the control input. The equivalent compensation was brought in the control to suppress the disturbance. Finally, the propose method was used to design a controller with a disturbance observer for an aerial camera mirror to achieve image motion compensation control. The experimental results show that as compared with advanced PID method, the compensation control algorithm based on the disturbance observer can reduce the forward image motion residuals by about 40%- 60% under the same disturbance. In conclusion, the method improves the compensation precision and the robustness of compensation control for forward image motion of the reflector in the aerial camera.