Abstract: Due to the strong nonlinear thermal-mechanical coupling procedure, the numerical simulation of welding stresses and distortion using 3D thermal-elastic-plastic finite element method takes very long computational time.In order to improve the speed of computation, a 3D dynamic substructure method, which takes the characteristics of welding problem, was developed.Noting that the region of fusion zone (FZ)and heat affected zone (HAZ)which exhibits strong nonlinearity by direct heating was limited in a very small zone compared to the size of the model to be analyzed and the remaining part far from the heat source is mostly linear, the 3D thermal-elasticplastic computation for the whole size of the model can be remodeled to the combination of a large linear problem and a small but moving strong nonlinear problem.In the 3D dynamic substructure method, the FZ and the HAZ remain nonlinear, whereas the remaining part of the model is treated as substructures which are linear.Moreover, the sizes of the substructures are also changing with the moving heat source.The simulated residual stresses and distortions using the substructure model are compared with the results of the full model and the experiment.The result shows that the substructure method is an effective method in reducing computing time with precise results in the welding region.