A diode clamping three-level inverter discontinuous PWM modulation method is characterized in that a small vector participating in output voltage synthesis does not have a redundant state; a switchingsequence have give segments in one PWM period; midpoint voltage balance is controlled by adjusting the action angle interval of an upper small vector and a lower small vector; according to the numberof a sector cell where the output voltage of the inverter is located, three spatial vectors participating in the output voltage synthesis are selected, and a corresponding midpoint current flow direction symbol is obtained from the inverter three-phase current when the lower small vector functions; a midpoint voltage deviation is multiplied by the midpoint current flow direction symbol and then enters a PI regulator for closed-loop control; the PI regulator outputs a small vector action angle interval adjustment signal, and the midpoint voltage balance control is realized by adjusting the action angle intervals of the upper small vector and the lower small vector. Compared with a commonly used 7-segment continuous PWM modulation method, the method reduces IGBT operation frequency by 28.6%, achieves a purpose of reducing the switching loss, and satisfies the midpoint voltage balance requirement.