This paper proposes a new large span half steel-plate-reinforced concrete (H-SC) hollow roof structure for nuclear power plants. The roof composes of 23 I-shaped H-SC beams. Each H-SC beam consists of a steel plate assembly (a bottom plate, a web plate and a short top plate), which is cast inside an I-shaped reinforced concrete beam. This novel system not only has an equivalently high bearing capacity, stiffness and lower gravity load comparing with conventional RC roof, but also can be conveniently constructed by using the bottom plates as formworks. The numerical simulation was conducted to demonstrate its mechanical capacities and the influence of construction process. Firstly, a finite element (FE) model for the H-SC composes was built and a one-third scaled 12 meters large-span H-SC beam was tested to validate the proposed FE model and analyze the steel-concrete-interface bond-slip. Then, the numerical simulation was conducted to assess the effect of the construction process on the mechanical performance of the entire roof structure, in which the deactivation element and trace element techniques were used to simulate the deformation induced by the construction process. The results show that the deflection induced by the construction process accounts for 87% of the final deflection.