Abstract: To improve energy efficiency, structural lightweight has gained wide attention. For shipbuilding, thin welded structure is widely used as superstructure. Since the influence of welding deformation on the fatigue strength of thin welded structure is unknown, classification rules do not allow using plate with thickness smaller than 5 mm. Based on the case on a cruise ship deck, the initial welding deformation is fitted at multiple sections. The finite element software ANSYS 15.0 is used to obtain the strain and hotspot stress at the specified section. The results show that the effect of welding deformation on the fatigue strength of welded structures can be well evaluated.