Abstract: In order to study the nugget formation during resistance spot welding procers of three-layer steels with different strength and thickness,asymmetric electrodes were utilized to improve the nugget size and weldability.Finite element analysis was used to investigate the current density,temperature change and nugget sizes of the thinner side.Experiments were also carried out to analyze nuggets sizes at different welding time.The welding lobes under symmetric and asymmetric electrodes were established.The results showed that the current density and temperature field of the thinner side could be changed significantly as asymmetric electrodes were applied,which could facilitate the formation of nugget and widen the weldability of three-layer sheets.