In order to improve the safety and reliability of power grid operation, an intelligent judement method for the last circuit breaker in HVDC project including bus-tie switch is proposed. An equivalent model and graph theory model for the last circuit breaker of AC field including bus-tie switch is set up, in view of the N bus-tie switches which are inserted in each AC bus, the AC bus is abstracted as N+1 nodes, and the nodes are connected by bus-tie swich. Taking line convergence joint as starting point and converter as the finishing piont, by way of searching the set of cut edges between starting and finishing point in the graph theory model, the problem that using conventional logic design can not realize the judement of last breaker of the full AC filed including bus-tie switch under multiple power transmission mode is sovled. Theoretical analysis and engineering case results show that this method can make the engineering application programming and debugging much easier, effectively avoid the risk of functional changes during the project expansion, and ensure the safe and reliable operation of power grid.