To solve the problem of robust fault diagnosis in satellite attitude control system,based on UIO,a nonlinear UIO(NUIO) is proposed to dealt with actuator and sensor faults.Considering the external disturbance and uncertainty of the nonlinear attitude control system,a new model for the system is established.By using H-infinity control and linear matrix inequality(LMI) approach,the NUIO matrix is obtained.At last,the diagnosis simulation of satellite attitude control system with actuator and sensor faults validates the feasibility of the proposed method.