Abstract: The welding deformation control of rail vehicles determines the assembly accuracy of the vehicles. However, the optimal clamping scheme determined based on traditional experimental methods has a higher cost, while numerical simulation calculation methods have shown significant advantages in welding deformation control. The study takes SUS301L stainless steel vehicle chassis as the research object and adopts the research method of "sequential thermal coupling+inherent strain calculation". Firstly, typical joint forms passing through the vehicle chassis were extracted, a local finite element model was established on this basis, and sequential thermal coupling calculation was carried out. Then, the inherent strain of the local model was extracted and loaded into the vehicle chassis welding simulation to calculate the welding deformation under different constraint states. The results showed that: (1) the simulated welding temperature field distribution trend is consistent with the actual welding process, indicating that the double ellipsoid heat source can better characterize the temperature field of the welding process; (2) the residual stresses after welding in both the free state and fully constrained state were concentrated in the weld seam and its vicinity, with a peak Mises stress of 601MPa, resulting in significant welding hardening; (3) the vertical deformation of the chassis after welding in the free state and fully constrained state is 13.56mm and 2.605mm, respectively, and the welding deformation in the fully constrained state is well controlled. In addition, the maximum deformation under free conditions is located in the middle position of the chassis, showing obvious upward convex bending deformation, while the welding deformation under full constraint is located in the end area of the chassis, which is easier to control through clamping. This study provides a theoretical basis for optimizing the welding deformation control scheme of key structures in rail vehicles.