Three Phase Boost Type PWM rectifiers with great feature of unit power factor and bid-direction energy flow are widely used in variable frequency speed regulation system, meanwhile, they also become variable frequency system fault multiple links. Therefore, in order to reduce the adverse effects of failure on industrial production, their fault diagnosis work has received great attention. In this paper, the existing fault diagnosis method of the main failure of PWM rectifier is summarized. These methods are classified from the fault vector extraction and fault identification and location. The principle of each fault diagnosis method is introduced. The scope of application and reliability of the diagnostic methods were compared. The future research directions and trends of three phase boost type PWM rectifier fault diagnosis and fault early warning are pointed out.