To address the problems in the construction of offshore bridges and culverts such as the structures susceptible to waves, limited layout, and high cost of soft foundation treatment, this paper proposed a new technical solution for reinforced concrete and ultra-high performance concrete (RC-UHPC) composite slab frame culverts. With supporting engineering, the ordinary box culvert was selected as a comparison scheme for technical and economic analysis, and the design points and construction procedures of new structures were introduced. Based on the calculation results of the overall bearing force, the bearing performance of the top slab under different load conditions was analyzed, along with an investigation of the secondary internal force resulting from the shrinkage and creep effects of the beam slab and the overall temperature deformation of the structures. The results show that compared with those of the ordinary box culvert, the concrete usage of the RC- UHPC composite slab frame culvert is reduced by more than 40%, and the total cost drops by more than 10%. The high toughness and durability of UHPC enable the structures to avoid premature cracking and other damage, thereby lowering full life cycle costs. Its bearing performance caters to the design requirements under operating and extreme wave conditions. As secondary effects resulting from shrinkage, creep, and temperature are significant, corresponding design and construction control measures can be taken to reduce the adverse influences of secondary effects. The RC-UHPC composite slab frame culvert provides a new and more applicable option for the construction of bridges and culverts in wave-affected areas, which can provide a reference for subsequent similar engineering applications.