Austenitic stainless steel, owing to its good mechanical properties and excellent corrosion resistance, is widely used in petroleum, chemical, nuclear power and other fields. Welding is an extremely important manufacturing method in industrial production. When the thermal elastic-plastic finite element method (TEP-FEM) is used to simulate welding residual stress, especially in thick welded joints, a long calculation time is generally needed. Therefore, it has become an urgent problem to develop an efficient and high-precision computational approach to simulate welding residual stress. In this work, numerical simulation and experimental methods were combined to explore the effect of size on the calculation precision of welding residual stress of SUS316 stainless steel by the 2D axisymmetric model, in order to clarify the applicability of 2D axisymmetric model in the prediction of welding residual stress in pipe butt joints. This research can provide theoretical support for the development of computational methods suitable for engineering applications. Based on the finite element software MSC. Marc, the temperature field and welding residual stress distribution of three different sizes of pipes were calculated by 2D axisymmetric model and 3D model. The calculated residual stress distributions in the thin pipe model are compared with the experimental measurements. The results show that calculated residual stress by the 2D axisymmetric model agrees well with the 3D model. However, in the weld seam near the inner surface and the areas near the weld seam, a deviation on the residual stress distribution between in the 2D axisymmetric model and in the 3D model was observed, which is significant as the pipe size increases. For practical engineering applications, with the regardless of the stress problems at the beginning and end positions, the 2D axisymmetric model can be used instead of the 3D model to calculate the residual stress of the girth weld, which is very beneficial to calculation time saving.