In this paper global welding buckling distortion of a thin wall aluminum T joint is investigated. A thermo-elastoplastic model is employed to determine longitudinal residual stresses; analysis of thermal model and elastic-viscoplastic (Anand) model are decoupled. Molten puddle motion (speed of welding) is modeled by using birth and death element method and time dependent model. Three dimensional nonlinear-transient heat flow analysis has been used to obtain temperature distribution, and then by applying thermal results and using three dimensional Anand elastic-viscoplastic model, stress and deformation distributions are obtained. By applying residual stresses on a structural model and using eigenvalue methods, global buckling instability of the welded structure is determined. Some experiments are done for validating the numerical results.