In order to detect and diagnose multi-sensor faults of quad-rotor aircraft, a multi-sensor fault diagnosis method based on adaptive observer was proposed. Firstly, the sensor fault was regarded as the virtual actuator fault after the establishment of the aircraft dynamics model and sensor model, the multi-sensor fault detection and diagnosis system of quad-rotor aircraft was constructed. Secondly, a nonlinear fault observer was designed to realize multi-sensor fault detection and isolation, and the nonlinear adaptive observer was designed based on the Laypunov method to estimate the mutiple fault biases. Finally, the stability and parameter convergence of the adaptive laws were proved in the presence of sensor measurement noise. The experimental results show that the method can detect and isolate the faults of multiple sensors effectively, and realize the estimation and tracking of multiple sensors fault biases simultaneously.