In existing Petri-net based models for power system fault diagnosis，temporal information of alarm messages has not yet been employed at all or fully utilized，and the fault tolerant capabilities of these models are limited.Given this background，a fuzzy Petri net model capable of handling temporal constraints is presented and applied to power system fault diagnosis.The places in the Petri net are assigned time attributes so as to take the time-delay constraints of protective relays and circuit breakers into account，and a fuzzy weighted algorithm is employed to improve the fault tolerance capability.The IEEE 10-unit 39-bus power system is finally used to demonstrate the fault diagnosing method developed.Compared with some existing fault diagnosing methods，the method developed is able to adapt to topological changes automatically and has stronger fault tolerant capability at a little bit more computational cost.The method is applicable to on-line fault diagnosis of large-scale power systems.