Prefabricated cantilever structure is a new type of structure in mountain expressway construction. In this paper, a new numerical simulation model of prefabricated cantilever structure is established. The model takes into account the modularization and assembly of components and the interaction between structure and soil. Based on the developed model, the effects of two design parameters (steel plate thickness between column and cantilever and column concrete grade) on the mechanical properties of the structure were evaluated. The modeling and simulation results show that the two design parameters have a slight impact on the mechanical properties of the main components (such as columns and cantilevers), but the steel plate between columns and cantilevers can significantly improve the mechanical properties of the connection structure. The thickness of steel plate can only be set according to the structure and stress distribution at the connection position