The invention relates to a three-level converter neutral point potential balancing control method and device which can be used to realize the zero potential control of the neutral point potential and has important practical significance. According to the invention, the multi-carrier CBPWM method based on zero sequence voltage injection is adopted to realize the neutral point potential balancing control. The upper voltage and the lower voltage of a direct-current bus neutral point are acquired, the different of the two voltages is inputted into a sliding mode variable structure controller to obtain the zero sequence voltage, and the zero sequence voltage is superimposed to the original three-phase modulation wave, so the neutral point voltage balancing control effect can be realized. The scheme has advantages of fast response speed and good robustness, and can be adapt to working conditions of different power factors and loads.