In this paper,a pulse MIG welding machine is designed. The ARM chip of STM32F407 is used as the control core to expand the peripheral circuit,and the driving signal generated by UC3846 chip is used to drive the main circuit of the full bridge soft switch inverter. Based on the constant wire feed rate and the mode of arc voltage feedback regulat-ing duty cycle,the arc length control in the welding process is realized. This machine has the basic protection functions of overload,overheat and abnormal voltage. And the digital interface has the characteristics of convenient parameter adjustment. The welding technology test shows that the pulse MIG welding machine designed by the current and voltage double closed-loop control mode has good arc length adjustment ability,and the weld quality can meet the welding requirements.