Abstract: By being taken weld formation mechanism as research object, and the influence of LB(Laser Beam) and VPPA(Variable Polarity Plasma Arc) coupling effects on heat source characteristics and weld formation mechanism were analyzed in LB-VPPA hybrid welding of Al-Zn aluminum alloys. The results show that laser absorptivity is increased by the coupling effects of LB and VPPA. A shining zone exists at the root of VPPA, especially during direct current electrode positive period. The heat source with the advantage of smaller heat input and higher penetration depth can be achieved by combining slightly smaller VPPA current, higher orifice gas flow rate and suitable laser power, which can overcome the difficulty of keyhole weld formation on flat position in VPPA welding. Better welded joints are achieved by LB-VPPA hybrid heating source welding on Al-Zn aluminum alloys with thickness of 8 mm at VPPA direct current electrode negative current of 115 A, VPPA direct current electrode positive current of 155 A, orifice gas flow rate of 3.0 L/min and laser power of 1 000 W.