There will be current transients when the traction drive is switching between different PWM strategies.To assure smooth transitions,a set of switching methods of PWM strategies is presented,including firstly from asyn-chronous PWM to synchronous PWM,secondly synchronous PWM to SHEPWM,and finally switching between different carrier ratios among SHEPWM.Based on the output voltage spectrum characteristic and the modulation patterns fea-ture,simulation model is established.By analyzing and comparing the simulated waveforms of switching different mod-ulation modes,the right points of switching are determined,which are confirmed by the experiments on an AC traction system and the current transients are effectively avoided.The research provides a basis for the design of control system of AC traction experiment.