The construction of smart grid requires that the relay protection especially backup protection must have better adaptability. The paper proposed a self-adaptive minimum fault isolation method based on the fault location diagnosed by Centralized Substation Backup Protection System. The method for searching breaker tripping sequence based on Petri net is proposed. It can accurately find the breakers need to trip in local backup protection， breaker failure protection and remote backup protection and has good adaptability to different main connections and different operation modes. Centralized backup protection system forms the tripping strategy based on the position of fault element， the breaks status and operating signal of protection. It can isolate the fault quickly and minimize the blackout zone.