The mechanical interaction between welded panel and fixture has a remarkable influence on the distribution of weld–induced residual stress and distortion. Unfortunately, the influence of fixture is not generally included in conventional numerical simulations of welding process. In the present study, it is proposed that the numerical models in which the mechanical interaction between welded panel and fixture is considered as contact pair in the finite element analysis (FEA) of welding process. This could make the FEA of welding process more scientific and accurate. The fixture constraint plays an important role in accurate modeling of welding process. In the simulations, various mechanical constraint boundary conditions in welding process were thought about to establish the relationships of the normal and tangential mechanical interactions between welded panel and fixture. In Free model, the fixture restraint was not considered. In Mech model, the displacements of nodes where welded panel contacted with fixture were restricted in x, y, z directions. Hard model and Tabular model were contact models which included the fixture. In the normal direction, once welded panel and fixture were in contact, the transmitted contact pressure could be infinite in Hard model. While data pairs of contact pressure vs over–closure or clearance were specified to define a piecewise–linear relationship in the normal direction in Tabular model. A penalty friction coefficient of 0.3 was applied in tangential direction in both Hard and Tabular models. Fixture and welded panel were separated and the contact relationships were removed after the welding process in both Hard and Tabular models. The simulation results of contact models including fixture were more accurate, compared to models containing only welded panel with rigid retrictions. The distortiomode of welded panels under different fixture constrait conditions corresponded well with xperimental results. The differences between the distributions of transverse sresses on top and bottom surfaces f welded panel at the beginning of welding process had a crucial influence on the distortion mode f welded panel.