The invention relates to a three-level converter discontinuous pulse width modulation method, which lowers common mode voltage and eliminates midpoint voltage DC offset. The method comprises steps offirst, collecting three-phase voltages and three-phase current of a three-level converter and preprocessing, re-ranking three-phase voltages, predicting a phase current of a next switch period by using three-phase current and re-ranking, then obtaining all possible clamping modes according to re-ranked phase voltages, calculating midpoint current according to re-ranked phase current of the next period, determining a clamping mode according to a midpoint voltage control rule so as to control the midpoint voltage, in regulation, abandoning a base vector with a high common mode voltage so as to reduce common mode voltage, finally, calculating a modulation wave according to a duty cycle model of the clamping mode, comparing the modulation wave with the carrier type determined under the clamping mode, and generating a specific PWM switch sequence. The modulation method provided in the invention can balance midpoint voltage effectively and lower switch loss of the system.