In the process of the construction and installation of Hua-long Pressurized Reactor, the modular construction of the steel lining bottom plate has intensive welding operations, and there is often the need to roll over the components. In this process, the weld will be deformed due to the heat input generated by welding, and the weld will also bear the gravity, tension and shear force of the plate in the process of turning over. Under the above various stresses, it will lead to large or small deformation of the weld, and even bring large deformation or even defects to the welding product. In actual construction, the deformation caused by stress and strain is usually adjusted in the way of late orthosis, which will not only invest more manpower and resources, but also delay the normal construction progress. In order to ensure the reliability of weld quality in the process and optimize the problems caused by stress and strain in the modular construction of steel lining, this paper combined with the modular construction of the steel lining of Hua-long Pressurized Reactor unit in a power plant, carried out software simulation analysis of related welds, and provided technical analysis for the change of stress in the welding seam of the modular construction of steel lining bottom plate.