Being the core for attitude information measurement,the sensors onboard UAV can supply safe,reliable and comprehensive information,and their working status directly affects the safety of the plane. By means of fault diagnosis technology,we can realize early detection of faults,thus to avoid malignant accidents and enhance the operation safety and reliability of aircraft. In this paper,analysis is made to the working principle of the sensors onboard the UAV,and an analytical model of the execution mechanism of the UAV is established. Based on the model,the characteristics of the sensors are simulated. Then,a fault diagnosis algorithm,threshold-improved SPRT united ALG based on residual errors,is used for extracting the fault features from residual errors,thus to detect and determine the working status of sensors. Finally,a common mathematical model of actuator′s fault is established,and the fault characteristics of the sensor are simulated. The result shows that this scheme can effectively improve the accuracy of sensor fault diagnosis,and the fault diagnosis algorithm is effective.