Abstract: In the high-power traction drive system, due to the limitation of the maximum switching frequency of the inverter, multi-mode modulation is generally adopted in the full speed range. The smooth switching between different modulation modes has an important impact on the smooth operation of the whole system. A multi-mode switching strategy based on flux deviation vector was proposed for traction inverter with AC motor as load. The goal of this method is to minimize the torque impulse of the motor before and after switching, and only the modulation ratio information of the switching time is needed to quickly calculate the stator flux deviation vectors of any two synchronous modulations before and after switching in different phases. Combined with the realization method of multi-mode modulation, the optimal switching point with the smallest amplitude of deviation vector was selected. This method not only realize the torque ripple in the switching process, but also indirectly realize the optimization of current shock. In addition, it avoid complex calculation and analysis and had very good versatility. The simulation results verified the practicability of the handover strategy.