Based on the existing experimental data and the calculation results of finite element model, the residual stress of plate welding under the constraint and free boundary was simulated numerically.The results show that the residual stress in the heat-affected zone is significantly reduced by preheating, the reduction of the residual stress in the mother plate under the constraint condition is positively correlated with the preheating temperature, and the residual stress in the free boundary is basically not affected by preheating.Post-weld heat treatment reduces the longitudinal and transverse residual stress in the high temperature nonlinear zone (weld seam and heat affected zone). Under the constraint condition, the transverse stress changes significantly on the surface of the whole motherboard, while the longitudinal stress only fluctuates at the edge of the board in the free state.The constraint enhancement only increases the stress value, but does not change the stress distribution trend.The influence of plate end constraint on residual stress is unidirectional, and the influence of transverse constraint on longitudinal residual stress can be ignored.The size of the constraint remains the same, and the change of the distance from the constraint to the weld has little influence on the residual stress in the near-seam area. The finite element calculation can reduce the modeling size appropriately to improve the solution rate under the premise of ensuring a certain accuracy.