A three-dimensional finite element model has been developed to simulate the MIG P/S welding process of two aluminum plates. The finite element calculations are performed using ANSYS finite element code, which takes into account the thermal and mechanical non-linear material properties. The results of finite element analysis compared with those of experiment to show its validity in view of distortions. Parametric studies are carried out on the validated model to assess the effects of various factors on the final residual distortion. Large deformations, temperature dependent material properties are included in the model. Finally, the formulas of fitting curves of angular distortion transverse shrinkage, and longitudinal shrinkage have been proposed.