One of several solutions to enhance the weldability of aluminum alloy is removing the aluminum oxide layer on the surface by adopting variable polarity arc welding. The authors' previous experimental research on the variable polarity arc welding of aluminum alloy showed that reverse arc polarity has larger heat input efficiency than a straight polarity. Furthermore, the authors have already developed a numerical analysis model and suggested a methodology of estimating the heat input efficiency through a comparison between three dimensional molten pool simulation and experiment with regard to the variable polarity GTA welding. This research is a follow-up of the previous study, and it reveals the heat input efficiency of reverse polarity arc in aluminum welding for the first time through the suggested method. As a result, the heat input efficiency of reverse polarity is 3.8 times larger than that of straight polarity in aluminum welding. (C) 2019 Elsevier Ltd. All rights reserved.