Abstract: A single chip microcomputer application system for controlling of thynstor SMAW power source and wire feeder is introduced. The current feedback PID algorithm is used to obtain constant current static characteristics of the power source, and the voltage feedback PI algorithm is used to control wire speed of the feeder. The welding machine developed has many advantages such as good arc striking property, reliable welding stability, less line-voltage fluctuation influence, better parameter adjustment and easy operation. By means of a specification key the required welding specifications could be executed strictly.