Abstract: A variable polarity tungsten inert gas（ VPTIG） welding method was applied for welding 15 mm thick 2219 aluminum plates with a new designed groove form,and the welding process of backing weld + cosmetic weld 1 + cosmetic weld 2 was selected to achieve one-side welding with back. The experimental results showed that the weld was well formed and the internal quality was level 1. The microstructure of central weld area was uniform equiaxed dendrite,the grain size of the cosmetic weld was finer and denser than that of the backing weld. The grain size in the fusion zone was different,in which there was a narrow equiaxed grain zone and the grain in the heat affected zone grew obviously. The ultimate tensile strength of joints at room temperature reached 60% of the base metal and the elongation rate was more than 4%.The fracture path was along the weld fusion line in backing weld and cosmetic weld,which was related to the uneven microstructure and weak properties caused by solute segregation.