In this experiment, ABAQUS was used to simulate and analyze the welding temperature field, post welding residual stress and out of plane deformation of 6 mm thick T-joint double wire MAG welding. There are two kinds of constraint conditions: scheme 1 does not fix the bottom plate and the welding is free from deformation; scheme 2 fixes the bottom plate during welding and releases the fixation after cooling. The results show that the welding temperature fields of the two schemes are consistent under the same heat source; the angular deformation of scheme 1 is large, the maximum deformation is about 1 mm, the deformation of the bottom plate in the weld heat affected zone is about 0.2 mm, and the maximum residual stress is located in the weld center, about 235 MPa; the maximum deformation in scheme 2 is located in the weld center, but the area is small, the maximum deformation is located near the weld heat affected zone, about 0.3 mm, and the maximum residual stress in the weld center is about 180 MPa;The analysis shows that the welding residual stress and out of plane deformation can be reduced by fixing the base plate and releasing it after cooling.