The permanent-magnet (PM) synchronous motor (PMSM) takes advantages of small capacity, high efficiency, and high power density and have become commonplace in electric-vehicle driving systems. However, the excitation of PMSM cannot be adjusted, which restrains the PMSM from widening the speed range above its base speed. A PMSM with a variable magnetic reluctance field adjustment is presented in this paper. A new structure of the rotor is introduced, and flux-weakening (FW) principle is formulated. Analysis is discussed, including the force on the main PM, the movement process of the PM in the PM slot, the characteristics of the movement of the PM, and the FW performance of the new PMSM used for electric vehicles. The emulation analysis coincides with the test result, which verifies the availability and feasibility of the FW method for this kind of PMSM used for electric vehicles.