Differential mode voltage and common-mode voltage were generated at the motor terminals and winding because the PWM inverter output pulse voltage. The voltage reflections will be produced at the motor end, so that a large over voltage was take shaped at the motor end, especially when long-term inverter and motor cable connection, endanger safe operation of electrical equipment. In this paper, generating mechanism of the differential mode and common mode voltage by PWM inverter drive motor system will be analyzed, on the basis of the output RLC filter of the inverter to suppress the motor differential mode voltage, proposed a newly improved passive filter of the inverter output , and the design method parameters. The filter can play an inhibitory effect to co-mode and differential-mode voltage at the same time, the simulation results show the effectiveness of the filter design, provide a theoretical basis for the study of the filter inverter-driven system.