Abstract: The welding current, arc voltage and shape of SACTIG and VPTIG welding were collected by high-speed camena system and welding arc analyzer. The relation betwenn welding are stabklity and associated parameters during the passing zreo time of SACTIG and VPTIG welding current was analyzed. The studied results indicated that (50 Hz) SACTIG arc may go out and reignite during changing polarity. While welding current increase to a threshold the arc will not go out. The higher reignition voltage will caused the longer arc going out, so the arc stability becomes worse. If reignition voltage is equal to arc voltage, the arc will not go out.