Abstract: Refill friction stir spot welding (RFSSW) of dissimilar alloys of 2 mm thick 5A02 aluminum alloy/TC4 titanium alloy plates was simulated by coupled Euler-Lagrange(CEL)algorithm.The effects of rotation speed and dwell time on the temperature field, equivalent plastic strain field and material flow during RFSSW were analyzed.The results show that at the initial stage of welding, the heat accumulation is obvious and the heating rate is relatively fast. As the welding process continues, the heat generation form transfers form friction heat to friction and plastic deformation, and the heating rate slowed down.Under the stirring tool rotation speed of 2000 r/min, plunging rate of 1mm/s, plunging depth of 1.9 mm, retracting rate of 1mm/s, dwell time of 0 s, the peak temperature of nugget zone at the Al alloy side reaches 558 ℃and the maximum equivalent plastic strain is 120. In the simulated process range, the peak temperature of the nugget zone is proportional to the rotation speed of stirring tool.The effect of dwell time on the temperature is not obvious.