Abstract: A full digital multi-function square wave welding inverter based on ARM was developed. To achieve the efficient energy transformation,double inverter structure was adopted in the main circuit,while full-bridge inverter circuit topology was used in the primary inverter circuit,and the secondary inverter was with double parallel half-bridge inverter circuit structure. The LM3S8971 ARM microprocessor with Cortex-M3 kernel was used as the cybernetic core for the full-digital control system. Through the current closed-loop feedback control and digital PID regulation,the constant current output characteristic of the primary inverter circuit was obtained,while a variety of output current waveforms could be extracted through digital low frequency modulation for the secondary inverter circuit. A digital control panel with double-core structure based on ARM and CPLD was designed to realize the digitization of human-machine interaction. Both performance test and actual welding process test indicate that the developed welding inverter was with such advantages as perfect dynamic performance,flexible control,convenient operation, and reasonable and feasible design.