Abstract: Under the same average welding current and welding voltage, by regulating the different based current and peak current, the Al-Mg alloy was welded with Al-Mg filler wire.The photos of welding arc were obtained by using high-speed video photography.Peak current has great influence on the shape and characteristics of the arc.With increasing the peak current value, rotated arc appears and pulsed rotated metal transfer behavior occurs.Based current has little influence on the arc shape.Base current is the important parameter for keeping arc burning.At pulse off time, it must be given base current value which is large enough to keep the arc burning stably.In this study, the arc shape is defined by arc length, arc width and arc portrait cross-section area, which will be influenced by the weld current.Peak current is important parameter of arc temperature and pulse energy.The study shows that when the arc is burning at pulse on time, the arc length, arc width and arc portrait cross-section area increase with raising peak current.