Neutral Point Clamped Three-Level Inverter (NPC TLI) is widely used in medium and high voltage speed regulation systems, grid-connected power generation and other fields because of its low harmonic content, small voltage stress of switching devices and good fault tolerance. Neutral point potential balance control is an important guarantee for NPC inverters. Neutral point potential imbalance will increase the harmonic rate of output voltage and current, and will also greatly reduce the service life of DC side capacitors. This paper proposes an improved neutral point potential balance control method with zero-sequence component superposition. By establishing the topology of NPC three-level inverter and the mathematical in detail switching function, the reasons for the neutral point potential imbalance are analyzed in detail, and then the relationship between the zero-sequence component and voltage of the DC side capacitor is derived. This method is not only simple to calculate, but also can well realize neutral point potential balance control. This results of the simulation prove the effectiveness and correctness of the proposed method in off-grid and grid-connected.