Abstract: By using finite element program Abaqus, the butt-welding process of 390 mm 20MnMoNb super-thick plates for manufacturing the tube-sheet of a Chinese ethylene oxide reactor was simulated.The distribution of welding residual stress and deformation was obtained.The welding grove was double U-shape and it was welded alternatively on both sides by turning the plates regularly with large cranes.In order to avoid the excessive deformation of the plates, external loads were applied on the plates away the joint.According to the simulations, compressive residual stress has been generated within the plate, while tensile stress has been found on the external sides.By applying external load, deformation was controlled effectively.The more load is applied, the less the plate will deform.However, the residual stress will increase as the external load increases.Therefore, the balance between deformation and load should be considered.