Abstract: In the presence of actuator faults in attitude control system of satellite, a method of sliding mode fault tolerant control based on sliding mode observer was proposed. The estimation of attitude and angle rate was obtained via a sliding mode observer, and an iterative learning algorithm was utilized to update the switching gain of the sliding mode term. Considering actuator faults as unknown dynamics, a method of sliding mode fault tolerant control which is insensitive to the actuator faults of attitude control system of satellite was presented. By using the system, input and state information, unknown dynamics was estimated based on which a sliding mode control law was designed. Finally, the numerical simulation result demonstrates the effectiveness of the proposed fault tolerant control method.