The invention discloses a novel modulation strategy of a three-level NPC converter. The strategy comprises the following steps of step1, defining two groups of complementary three-phase modulated waves; step2, calculating the expression of the first group of three-phase modulated waves in the step1 and calculating a duty ratio of the first group of three-phase modulated waves; and step3, calculating the expression of the second group of three-phase modulated waves in the step1 and a corresponding duty ratio; in two switch periods, comparing the first group of three-phase modulated waves and the second group of three-phase modulated waves with the up and down carrier waves of the converter, and then outputting a final PWM pulse to the three-level NPC converter. In the modulation strategy, based on a three-phase sine voltage, one group of the modulated wave is supplemented; and the two groups of modulated waves alternately act on the three-level NPC converter in the two switch periods soas to realize neutral-point potential balance under a whole modulation degree and a full power factor. Compared with a dual-modulated wave carrier wave PWM modulation strategy, the modulation strategy of the invention has a simple algorithm and is easy to realize.