Abstract: For problems that there are common-mode voltage, over voltage and neutral-point potential imbalance simultaneously in power supply of inverter to motor through long cable, generation mechanisms of common-mode voltage and over voltage were analyzed as well as effect of neutral-point potential imbalance on common-mode voltage. A strategy of neutral-point potential balance control and common-mode voltage suppression was proposed, namely adding the fourth leg to traditional three-level inverter, controlling current of the fourth leg to realize neutral point potential balance and optimizing SVPWM modulation strategy of main circuit to restrain common-mode voltage. Effectiveness of the strategy is verified by Matlab simulation.