Abstract: The sequential thermo-mechanical coupling method was used to establish the model,and through the orthogonal experiment, the effects of welding speed, overlap amount and stirring tool rotation speed of friction stir lap welding on the residual stress of Al-Mg dissimilar alloy were analyzed by ABAQUS software. The optimal process parameters were obtained. The simulation was verified by tests. The effects of welding speed and overlap amount on the residual stress were studied. The results show that the optimal parameters of friction stir lap welding were welding speed of 60 mm·min^-1, overlap amount of 60 mm and stirring tool rotation speed of 1 400 r·min^-1. In different welding processes, the simulation of thermal cycle curves and residual stress were consistent with the experimental results, and the relative errors were less than 7.5% and 8.4%, respectively, which verified the accuracy of the simulation. The maximum residual stress appeared at the overlap surface at the end of the weld, and the maximum longitudinal residual stress in the optimal welding process was 137.7 MPa. Compared with the rotation speed of the stirring tool, the welding speed and the overlap amount had a great influence on the residual stress. With increasing welding speed, the peak value of the longitudinal residual compressive stress increased,and the range of compressive stress became narrower; with increasing overlap amount, the peak value of longitudinal residual compressive stress decreased and the range of compressive stress became wider.