School of Electrical Engineering，Southwest Jiaotong University，Chengdu610031，China

A layered fuzzy Petri net method for power system fault diagnosis is proposed.It can consider temporal constraints of protection and breaker actions.The fuzzy Petri nets models for line and bus are described firstly.The unary and binary temporal constraints in the fault diagnosis of power system are then analyzed.The method of temporal checking is proposed to improve the current of fault diagnosis.By the crossing temporal checking on both sides of lines，the action probabilities of protection and breakers can be modified，the malfunction and refusal-operation of protection also can be detected with forward temporal checking.The testing results of multiple cases illustrate that the fuzzy Petri net is effective.