For high-speed permanent magnet synchronous motor, smaller input voltage harmonics are usually required to reduce loss. Generally, the output voltage pulse of the inverter can pass through an LC filter before the motor side to reduce total harmonic distortion, but the influence of the frequency ratio on the parameter design of the LC filter has not been considered in the existing studies. Based on three-level inverter, a design method of LC filter suitable for high-speed and low frequency ratio is proposed, and the parameter design formula is derived. However, the introduction of the LC filter changes the mathematical model of the controlled object. Then, a complex vector current controller considering LC phase delay is designed, which is suitable for LC system in low frequency ratio. Compared with the traditional PI controller, it can achieve lower response delay. Finally, the effectiveness of the proposed strategy and current controller is proved by simulation results.