The aim of this study is to analyze welding behavior of AA3003 in resistance projection welding (RPW). In automobile industry, the demand for aluminum is increasing to reduce the weight of vehicle. However, owing to the high thermal and electrical conductivities of aluminum, welding behavior is different with conventional steels. The RPW is one of resistance welding processes, where a projection is formed on part of a plate to induce melting in a low current area. Although RPW is widely used, the research is limited compared with resistance spot welding, and few researches deal with application of RPW to aluminum. In this paper, the effect of various welding variables on the RPW behavior of aluminum is investigated by constructing 3D finite element (FE) model, which considers heat loss and projection stamping process using Abaqus (6.13ver). Finally, we compare nugget size between welding experiments and FE analyses, and determine welding variables that affect welding behavior.