Abstract: As a typical “super engineering”, the economy of nuclear power plant is an important indicator to determine its competitiveness in the global power market. Due to the large overall size of the thinwall largespan box structure of a project, the traditional construction process cycle of integral lifting in place after external assembly of the plant is long. It has a great impact on the critical path of project construction and can not meet the requirements of the overall construction progress of the project. Therefore, it is necessary to study a new process idea of layered assembly and lifting in place. This process can realize the intersection and parallel of civil construction and installation construction, and ensure the smooth realization of major milestones of the project. But the thin-wall large-span box structure itself has some problems, such as low stiffness, instability, easy to produce large deformation in the lifting process, which is the key problem to be solved in the modular construction process. In order to solve this problem, the anti-deformation design of the whole lifting of a thin-wall large-span box structure was carried out from the two directions of fixture design, balance beam and lifting point design. In order to get the ideal antideformation tooling design and lifting point design, several times of simulation were carried out. According to the simulation results, the causes were analyzed and the design was optimized. After obtaining the preliminary design scheme, the overall deformation of the balance (lifting) beam and the local stress of the lifting point were analyzed by numerical simulation, so as to improve the design scheme of the balance beam, optimize the spatial arrangement of the lifting point, and obtain a simple and universal design scheme. After determining the optimal design scheme of balance beam and lifting point, combined with numerical simulation, the antideformation fixture was adjusted (such as: adjusting the arrangement and quantity of inclined brace, local reinforcement) to control the deformation of the overall lifting process, and ensure that the structure meets the requirements of safety and design deviation in the overall lifting process. Through finite element analysis and design optimization, a set of universal anti deformation design scheme was finally obtained, and sensors were installed in the construction process to monitor the deformation for further verification. The results show that the anti-deformation design scheme can optimize the stress of the thin-wall large-span box structure during lifting, reduce the deformation caused by the overall stress, and overcome the technical problem of modular construction of the thin-wall large-span box structure.