Abstract: In order to improve the efficiency of the substation fault diagnosis with multiple protections,the proposed method describes prot ection grades by varied weights of the transition vector in the Petrinet models.According to relays and circuit breakers,special markings are produced in the diagnosis results that enhance the identifying capability of error information.The process of fault diagnosis is accomplished by algebra matrixes calculation.An simulation on actual substation fault diagnosis process indicates that the i mproved method has fast calculation speed and high veracity.