Based on residual voltage transformation method for short-circuit calculation， a unified approach has been proposed for transient stability calculations under unbalanced operating conditions of power system. The proposed method combines the advantages of both adaptive modeling in a，b，c phase components and 0，1，2 sequence coordinates with high calculation efficiency. The equivalent positive sequence admittance matrix is derived with matrix translation in place of the traditional sequence network connection， which is the interface with generators in stability simulation. The new method is suitable for both a，b，c coordinates and 0，1，2 symmetric components coordinates. It can deal with multiple faults and element with unbalance parameter as well. The simulation results show the new method is simple and effective.