Abstract: In order to realize automatic control of plasma arc welding process, the control system using the OMRON CP1H PLC as the core combined with touch screen was designed in accordance with the plasma arc welding requirements in the paper. Characteristics of plasma arc welding process, together with the control object and control sequence of the core PLC in the welding process were analyzed. Two independent welding power sources were selected as pilot arc and main arc power sources to enhance the stability and anti-interference ability of the system. RS-485 was used for data transmission between PLC and touch screen, and centralized control and adjustment of corresponding welding parameters was carried out. The human-machine interface of touch screen was constructed with Easy Builder 8000 design software and the composition and relationship of the whole system was systematically introduced. Finally, two welding processes, plasma welding without filler wire and with ERNi-1 welding wire were used as the filler material to butt weld N6 nickel plate with 6 mm thickness. The weld formed well. The system ran safely and reliably and had high maintainability. It realized automatic control of plasma arc welding process.