Permanent magnet synchronous motor (PMSM) is a time-varying system with strong coupling and nonlinearity. The traditional harmonic voltage compensation method is difficult to automatically optimize the voltage parameters. In order to solve this problem, a fast signal processing method based on global search extreme point is proposed, which can dynamically and efficiently suppress the harmonic current of motor. The extreme seeking control algorithm can quickly lock the harmonic voltage amplitude and phase of the target order, and the compensation unit injects the corresponding vector voltage into the motor in real time to achieve efficient suppression of harmonic current of the motor. The experimental results show that this method can effectively suppress the low-order harmonics at multiple frequencies of permanent magnet synchronous motor.