Aiming at the common stator winding interturn short circuit fault in the life cycle of traction motors, a fusion fault method, based on fault model of three-phase stationary frame and positive and negative sequence fault model, is proposed. Capitalizing on particle swarm optimization, the fault characteristic parameters are obtained. A fault diagnosis of traction motors is performed by simulation and the efficacy of this method is validated. The results indicated that the implementation of this fault diagnosis method is not only capable of diagnosing with high precision under fault conditions, but also needs fewer parameters.