The influence of the dead-time on the output wave of inverter in a dinital UPS is analyzed in detail.Meanwhile in order to illustrate vividly the influence of the dead-time on the output voltage of inverter has something with the way of the output current of inverter,and analyz the work principle of single phase full bridge inverter,also get some influences about the dead-time on the output voltage from the picture of the dead-time and distortion of output voltage wave.A effective compensatinn method is presented.