Abstract: In order to solve the problem of welding deformation of large-size body side frame welding assembly, this paper proposes a welding deformation control idea based on welding sequence optimization by analyzing the relationship between welding sequence, welding stress and welding deformation of its basic welding unit T-shaped welding structure. The simulation results show that when welding four-pass joints, subsequent welding passes effectively perform heat treatment on prior welds, thereby reducing the peak residual stress in preceding weld seams. This stress reduction directly corresponds to decreased welding deformation. In this study, compared with conventional symmetrical and sequential welding methods, the proposed welding sequence of welding joints with smaller deformation under the free state firstly and then welding joints with smaller deformation under the constrained state of the clamping can effectively reduce welding deformation. Using the optimized welding sequence, the welding distortion decreases by 50.7%, from 6.5 mm to 3.2 mm.