Abstract: It can change magnitude and direction of fault current of distributed network after distributed generation was connected to power distribution system, which made fault diagnosis of power distribution system complicated. For the above problem, a fault diagnosis method of distribution network based on power direction criterion and Petri net was proposed. The method uses uploading and measured double fault information to realize redundant error correcting, and can accurately and quickly diagnose fault areas, so as to improve fault diagnosis accuracy and fault tolerance of distribution system with distributed generation. At the same time, the method uses unique graphic description and parallel processing ability of Petri nets to ensure universality of fault location model and rapidity of fault diagnosis. The example simulation results verify feasibility and effectiveness of the proposed method.