Abstract: The authors developed a special discrete closed loop system for controlling pulsed MIG welding arc,named QH-ARC System Model 102.It was demonstrated that the static and dynamic characteristics of the control system are excellent.The operating points of pulsed arc are maintained at the constant current portions of the step-like out-put characteristics,and this results in extended range of applicable welding current for spray transfer with minimum spattering.The arc length signal is sampled at every pulse duration so as to ensure stable arc length against any disturbance.Moreover,the pulse parameters can be automatically optimized over a wide range of wire feed speed.Thus this system leads to a new developed MIG technique with pulsed or programmed wire feed,which can be used for positional welding,heat input control,bead formation control and even closed loop control of penetration.It has also great potential in robot application.In this paper,the block diagram,circuit arrangement,principle of operation and some welding effects of this closed loop controlled pulsed MIG welding system are described.