Abstract: A simple and reliable microcomputer hardware and software system for controlling SCR arc welding rectifier is described in this paper.It is discussed how to use the proportional-integeral-derivative (PID) algorithm to realize the controlling program for the various statio characteristics,such as constant current,constant voltage,drop etc..By means of experimental analysis,a good method for controlling short-circuit transfer in manual arc welding with covered electrode was found aut.The result of welding tests shows that this welding power source has more advantages than the same kind of welders under analog control in decreasing spalter,stablizing the arc and operating convenience.