Compared with the conventional buck-boost three-level inverters, the Z-source neutral-point-clamped (NPC) inverters have more simple structure with improved output waveform quality. But the neutral-point potential unbalance problem is still a drawback for their applications. Based on the research of SPWM modulation method and the analysis of the effect of the shoot-through states on the neutral-point potential, this paper proposes a neutral-point potential balancing method by adding the shoot-through offset which can be applied to the constant boost control and the third-harmonic-injection control. This new method is simple and has the advantage that the neutral-point potential unbalance problem can be improved with the high voltage gain, which is verified by simulation results.