A CO,2, gas shielded welding machine based on dsPIC30F4011 is designed. In order to reduce the loss of power switch tube and improve the electromagnetic inter-ference of welding machine, the main circuit adopts the phase-shifting full bridge soft switch circuit,which makes the super forearm realize ZVS with constant frequency and pulse width, and the lagging arm realize ZCS with constant frequency and width,which improves the overall performance of welding machine. The design of the main transformer is the key and difficult point. It is analyzed and designed from three aspects: the selection of magnetic core material,the selection of magnetic core model and the design of coil winding.dsPIC30F4011 is selected as the main control chip in the control circuit to monitor the working state of the welding machine in real time. According to the DSC hardware circuit,the corresponding software program is designed. The software program adopts modular design,including wave control software design,program control software design and wire feeding software design. Finally,the goal of small welding spatter,precise timing control and constant wire feeding is achieved.