Abstract: As an effective supplement to ground transportation, metro plays an increasingly important role in urban life, who has the advantages of green, pollution-free, punctual and strong carrying capacity. A couple of 3D Gauss and double ellipsoid heat source were adopted, and the inherent strain method was used to simulation the welding deformation of the metro traction beam under different constraints. Based on the simulation of the existing constraints, three other constraints were designed. The results show that the simulated results through the inherent strain method are in good agreement with the measured results. The maximum deformation in x-direction and z-direction occurs in scheme 2, which are 2.46 and 13.13 mm, respectively. The deformation in y-direction is stable at about 1.63 mm. Put the angular deformation with maximum variance of change rate as the evaluation criteria, scheme 4 is the most reasonable, and the minimum angular deformation is 1.21 degree.