Recent discoveries of stress corrosion cracking at welded joints in pressurized water reactors and boiling water reactors have raised wide concerns about the safety and integrity of plant components. It has been recognized that residual stress and applied stress on their surfaces largely increase the expanding risk of initial stress corrosion cracking. Therefore, it is very important to investigate the welding residual stress in welded joints. It is very expensive and time–consuming to measure the residual stress, and sometime is impossible. As an alternative approach a computational procedure on the basis of finite element method is effective in solving non–linear problems such as thermal and mechanical nonlinearity in a welding process. Accurately simulating welding residual stress not only needs generally a long computational time, but also strongly depends on the analyst’s experience and know–how which is a main hindrane for the welding process simulation. Therefore, it is an urgent task to develop a time–effective numerical simulation procedure to calculate welding temperature field and residual stress distribution. In this study, a new method on the basis of the vaiable length heat souce was developed to simulate the welding residual stress in a multi–pass butt–welded joint of austenitic stainless steel. Meanwhile, the experiment was carried out to obtain the welding residual stress in the utt–welded joint. Comparing the simulated with experimental results, it was found that this method could not only save a large amount of computational time but also provide a highly accurate numerical result for the residual stress in multi–pass butt–welded joints.