Abstract: Aiming at the problem of the third fundamental frequency fluctuation of the midpoint potential of VIENNA rectifier, the mathematical model of the midpoint current is established. The midpoint fluctuation form is analyzed, and the mathematical reason of midpoint fluctuation is pointed out by analysing the midpoint current mathematical model. To overcome the limitation of the traditional fixed adjustment factor control method to suppress neutral-point voltage fluctuation, a hybrid suppression method combining dynamic adjustment factor and capacitance deviation adjustment is proposed. This method realizes the automatic suppression of the midpoint potential fluctuation through looking for the tables for the deviation adjustment and the dynamic adjustment factor expression within the six sectors which is injected into the three-phase modulation waves, and further modified hybrid suppression method can effectively suppress the large fluctuation hybrid of the midpoint caused by asymmetry of the capacitance parameter and the unbalanced load. The experimental results verify the feasibility and validity of the strategy.