A new dual control strategy is proposed to solve the problem of large output voltage ripple of traditional three-phase three-level inverters with small duty cycle mode. By controlling the voltage of the DC bus and the duty ratio of the inverter, this strategy can realize controllable adjustment of the output DC voltage in a large range. The MATLAB/Simulink system simulation model of 200 kV/15 A inverter DC high-voltage power supply was established, and the above control strategy was used to realize that the ripple was less than ±1% when the output voltage was 200 kV and 20 kV respectively. It is verified that the new control strategy is effective in a wide range of output voltage. The output voltage ripple can meet the load requirements.