Abstract: Air plasma cutting machine requires high open circuit voltage,but arc voltage is half or one third of it.So far the duty cycle for the high power SCR arc plasma cutting machine is low,which results from bigger angle of lap,and power factor goes down.To ensure rated power output,more input current is required and the coil is heated heavily.In this paper,the topology is changed and the capacitor bank is connected with primary coil in series.The idle work is also compensated to improve load power factor.Therefore,it can reduce input current of transformer primary coil,power factor and duty cycle are raised.