Abstract: The resonant soft-switching inverter arc welding power source uses LCL-type structure in the main circuit,and selects phase shifting pulse wide modulation technique in the control system.The main circuit principle of the arc welding power source is introduced and the work procedure is analyzed in the paper.The new LCL main circuit can make full use of transformer inductance-leakage and eliminate duty cycle loss according to simulation and experimental results.The basic structure,circuit and work principle of the control system is introduced,which includes the UC3875 circuit set,arc voltage and current feedback circuit,IGBT driving circuit.The debugging and process experiment of the prototype are made.It is demonstrated by the experiment that the prototype has such characteristics as good stability and reliability,stronger anti interference ability,wide soft-switching range.The welding power source fits for TIG welding.