Abstract: A new microcomputer based mulitiple purpose SCR arc welding rectifier is introduced in this paper. On the basis of analysing the control system of the rectifier, reliable control models for constant current(C.C), pulse current and A.C. current output requirements of the welder have been developed. And, a special control system based on chip microcomputer processer and its assembly language program have been designed and built to realize these control models. The testing results show that the output characteristics of the new machine (such as the pulse wave form, the adjusting accuracy and range of the output current) are better than those of the commercial welder with conventional electrical circuits. This successful investigation facilitates the application of the microcomputer to welding equipment.