Abstract: As the power system capacity of airliner is increasing, brushless excitation has been applied to the aircraft generator. The voltage and current of rotating rectifier cannot be measured directly because of the elimination of carbon brushes and slip rings in excitation system, so the faults cannot be detected. There is an effective way to detect faults according to the features reflected in the stator field winding. Firstly, the fault mechanism of rotating rectifier is studied based on harmonic analysis. Next, the common faults of rectifier diode are classified and the aircraft generator simulation model is established to observe the generator output and stator field current. Finally, the feather of fault signal is extracted based on harmonic analysis, laying the foundation for further fault diagnosis of rotating rectifier in aircraft IDG.