Due to the strong nonlinearity of the servo drive, the stator current of permanent magnet synchronous motor (PMSM) contained a large number of higher harmonics and caused a large torque ripple. To solve this problem, a harmonic suppression method based on cascaded secondorder generalized integrator (SOGI) was proposed. Cascaded SOGI was parallel to current loop dqaxis PI controllers. The sixth harmonic component of dqaxis current was extracted by cascaded SOGI and injected into the output voltage of PI controllers, which could offset the harmonic in reference voltage. The simulation results showed that the distortion of current waveform had been greatly reduced by using voltage compensation method based on cascaded SOGI, which confirmed the effectiveness of the algorithm.