Abstract: Consider the structural design form of large-span thick plates and complex layout design requirements in NPP, taking a NPP as an example, the plate construction has certain difficulties due to the constraints of the aforementioned conditions, thus the truss steel bone-concrete composite structure is proposed. This composite structure consists of three parts: the bottom steel plate, the truss steel bone, and concrete, and based on a layered pouring method, the concrete are divided into three layers for pouring: 1) pouring the bottom concrete slab; 2) pouring the concrete beams; 3) pouring the top concrete slab. Then, a comprehensive bearing capacity performance analysis of the construction phase of the composite structure is conducted: based on the layered pouring, the entire construction process is divided into seven analytical steps, adopting a gradual loading method and accumulating stress, utilizing the technology of live and dead cells to analyze the load-bearing performance of composite structures, and benchmark them against standard limits. The results show that the bearing capacity of the composite structure during the construction phase meets the design requirements. The overall load-bearing performance analysis of the NI was conducted, considering the secondary bending performance of the truss steel bone structure, the bearing capacity performance of the composite structure was analyzed in detail. The results show that the load-bearing performance of the combined structure meets the design requirements for the service stage.