Based on the mega plate joints appeared in the construction of Guangdong Science Center, creating model, numerical simulation and analysis of residual stresses on plate joints has been performed by APDL program. The mechanics performance of plate joints in mega steel structure is very complex, and the welds have been mustered together, so the welding residual stresses in the plate joints are very large, and they are can't be eliminated easily, and the property of welding residual stresses in the plate joints should be researched and analyzed. And because of the welds are very small relative to the mega plate joints, it is hard to create model. In addition, the birth/death element need use hexahedron grid, so mapped mesh was used by APDL program. And the residual stress simulation was performed with good results. With the method of coupling between thermal and structural field and the technique of element birth/death, ANSYS was applied to calculate the welding residual stresses, and the properties and reasons of residual welding stress and residual welding deformation were analyzed. The paper may be helpful to the other similar simulations of residual stress in the future.