A fault diagnosis method is designed for the distributed flight control computer of UAVs. A method combining hardware redundancy with the model's analytical redundancy is proposed for the fault diagnosis of the computer's external sensors, external actuators and internal functional modules. By designing the diagnosis architecture, the fault detection and isolation for the computer's external sensors, external actuators and the internal digital controller of the flight control computer can be effectively realized. It solves the problem that the traditional single fault observer cannot diagnose the computer's internal faults, and improves the coverage rate of fault diagnosis and the reliability of the flight control system.