Abstract: A finite element analysis model was established for resistance spot welding of aluminum alloys, and a contact resistance model based on micro-contact theory was employed to describe the contact resistance at the faying surface. The variation of contact radii at electrode/workpiece and workpiece/workpiece interfaces, in addition to the distribution of stress, current density and temperature at the faying surface during spot welding process were all obtained. Experiments were conducted to examine the process of nugget initiation and growth. Comparisons show that the calculated and experimentally measured results agreed with each other very well, which validate the correctness and suitablilty of the contact resistance model in modeling the resistance spot welding of aluminum alloys.