A novel synchronization modulation technology based on flux trajectory tracking control was presented to resolve the high PWM harmonic problem because of using low switching frequency inverter for high power AC driving system. The optimum switching angles were got off-line according to the principle that the total current harmonic of motor was least, which derived the trajectory of stator flux. While the system was in working state, the flux threshold of special position was calculated real-timely and the stator flux estimated was compared with the flux threshold, so the synchronization modulation based on stator flux trajectory tracking control was realized. The simulation and experiment showed that the method presented was feasible and right.