Many space-based camera and optical pointing and tracking systems require their line of sight (LOS) to be steady. The Inertial Pseudo-Star Reference Unit (IPSRU) is one of the effective machine which can enhance the sharpness of the camera. In this paper, we design an active disturbance rejection controller to reduce the influence of disturbance. The simulation result is achieved. Compared with the PID controller, the active disturbance rejection controller rejects the disturbance more effectively.