The permanent magnet synchronous motor driving system based on three-phase four-switch inverter had the problem of the torque ripple. Aiming at it, a torque ripple optimal control of the system was proposed. The torque ripple in the system was divided into low frequency and high frequency torque ripple. The low frequency torque ripple was generated by the voltage fluctuation of the DC capacitor, and a compensation scheme based on nonorthogonal coordinate transformation had been introduced to compensate it. For the high frequency ripple, analysis and evaluation of effects of different modulation strategies, and the optimal modulation strategy had been chosen. In addition, the linear modulation range was taken into account, and the DC capacitor voltage fluctuation of the system was considered. At the same time, an adaptive capacitor voltage offset suppression method was designed to extended linear modulation range. The experimental results showed that the new control strategy could suppress the torque ripple.