Abstract: By setting up a double pulse variable polarity plasma arc welding system, through process test of high strength aluminum alloy welding with double pulse VPPA (variable polarity plasma arc), weld formation and mechanical properties of welded joints of low frequency pulse modulation superposition high frequency pulse were studied. The results show that the low frequency pulse can obtain the fish scales weld by the periodic oscillating liquid molten pool. The high frequency pulse causes the arc more concentrated and improves effectively the energy density of the arc, thus enhance the arc force. Coupled oscillation of the double pulse strengthen the stirring of the molten pool, and refine the grain sizes of the aluminum alloy weld. The tensile strength of welded joints reaches 384.13 MPa, compared with VPPA welded joints, the strength is increased by about 10.21%. And the percentage reduction of area and percentage elongation of welded joints have been improved to a certain degree. The double pulse VPPA welding process improves the mechanical properties of the welded joints of the aluminum alloy.