Abstract: The AZ31B magnesium alloy and 304L stainless steel butt joint were obtained in laser-TIG hybrid welding. A new coupled heat source model was developed, which combined by double-elliptic planar distribution, double-ellipsoid body distribution and Rotary-Gauss body distribution model. The thermomechanical behavior and residual stresses distribution of the butt joint were analyzed by using finite element techniques. The results show that the temperature distribution of the dissimilar metal hybrid weld joint is different, and the residual stress on the 304L stainless steel plate is lower than that on the AZ31B magnesium plate.