The three-phase three-level VIENNA rectifier causes the current zero-crossing distortion due to the uneven voltage stress and voltage imbalance at the midpoint of the switch transistor, which reduces the overall performance of the system. Therefore, the causes of midpoint voltage imbalance and the influence of vectors on midpoint potential in the seven-segment algorithm are analyzed from the perspective of space vector, and based on the traditional SVPWM modulation, an improved space vector modulation strategy is proposed to reduce the output voltage fluctuation: In the same sampling period, a regulating factor is used to reasonably allocate the action time of positive and negative small vectors, thereby canceling the middle vector and maintaining voltage stability. In addition, the algorithm implementation is optimized by analyzing the relationship between the adjustment factor and the system modulation ratio. Finally, simulation shows that the midpoint voltage fluctuation of the control strategy is reduced from ±12 V to ±4 V compared with the traditional control strategy, which proves the correctness and effectiveness of the proposed strategy.