Different choices of IGBTs’ switching frequency of the PMSM inverter used in vehicle lead to different energy loss of the inverter. Meanwhile, they lead to different phase current harmonics, which result in different energy loss of the PMSM. Compared with traditional switching frequency design method, the optimal design method considers the loss of the PMSM as well as the inverter, proposing a minimum system loss switching frequency design method. Firstly, by establishing the IGBT model (Hefner Model) and the PMSM analytical model, obtain PMSM phase currents under different switching frequencies through simulating. The inverter energy loss is obtained at the same time. Then, the phase currents under different conditions are applied to the finite element model to obtain the distribution of the magnetic field strength H and the magnetic induction B, so that the PMSM loss can be calculated. Comprehensively, the variations of the energy loss of the PMSM and the inverter with the different switching frequencies are obtained. At last, the optimal frequencies under different conditions are calculated considering the overall loss of the PMSM and the inverter.