Abstract The ultimate compressive strength of unstiffened plates is very important from the design and safety viewpoint. However, the ultimate compressive strength of these panels will depend quite significantly on the initial welding distortions and residual stresses. Currently, most of the researches concerning the effect of welding distortions concentrate only on the maximum initial distortion amplitude. However, many evidences indicate that the welding distortion shape could also affect the ultimate compressive strength significantly. In this paper, we adopt a combination of the elastic large deflection theory and the rigid-plastic analysis, proposed by Paik and Pedersen and later was generalized by the present authors. Various factors including the initial deflection shape which affect the ultimate compressive strength of unstiffened plates are investigated.