Abstract: With the material of aluminum alloy 5A06, the weld pool and plasma plume dynamic behavior during laser scanning welding were photographed by using high-speed photography. The character of fluidity for molten pool surface and of plasma plume vibration were analyzed under conventional single laser beam and laser scanning welding.The research results showed that compared with Single laser beam, the oscillating laser beam can greatly enhance the stability of plasma, prolong the cycle, increase the direction of the molten pool flow at the same time, and improve the stability. On the whole welding molten pool surface backflow phenomenon did not occur. Dynamic pressure resulting from molten pool flow reduced the impact of the keyhole. The keyhole stability is greatly improved.