Abstract: The butt-welding process of 390mm 20MnMoNb super-thick plates for manufacturing the tube-sheet of a large scale ethylene oxide reactor was simulated by finite element program-ABAQUS.The residual stress and deformation in the welded tube-sheet are obtained.The welding grove was double U-shape and it was welded on both sides by turning over the tube-sheet continuously with a travelling crane.The effect of the turning numbers on the residual stress and deformation was investigated.The results show that angular deformation occurred in the tube-sheet and large tensile residual stresses is generated in the weld and the heat affect zone closed to the external surfaces of the tube-sheet, while compressive residual stress inside the tube-sheet.Both the residual stress and deformation decreased with the turning number increasing.When the turn number was above seven, the effect gets weakened gradually.