Abstract: Composite sandwich structure is widely used in lightweight design of rail vehicles. Traditional composite sandwich structure with a single aluminum honeycomb core has poor impact resistance, which is difficult to meet the application requirements. A rectangular aluminum grid structure is added into the core of the traditional carbon fiber/aluminum honeycomb sandwich structure to form the carbon fiber/grid reinforced honeycomb sandwich structure, and the drop hammer impact test and post-impact compression test are carried out at three typical positions, the intersection of the grid, the center of the single rib plate and the center of the grid. The carbon fiber/grid reinforced honeycomb sandwich structure is applied to vehicle roof. The simulation models of vehicle roofs of three different materials are established under the rockfall impact condition to analyze the mechanical properties such as specific peak load and specific stiffness. The results show that the carbon fiber/grid reinforced honeycomb sandwich structure has stronger impact resistance than traditional carbon fiber/aluminum honeycomb sandwich structure, with compression of approximately 34% higher and compressive stiffness of 52% higher after impact strength; The peak contact force, delamination critical load and dent depth at the intersection of the grid and the center of the single ribbed plate are significantly better than those at the center of the grid; Compared with the carbon fiber/aluminum honeycomb vehicle roof, the deformation of the carbon fiber/grid reinforced honeycomb vehicle roof under rockfall impact is reduced by 71.73%, and the specific peak load and specific stiffness are increased by 133.33% and 146.72% respectively. The carbon fiber/grid reinforced honeycomb sandwich structure has the advantages of both lightweight and strong performance, which is suitable as large-scale bearing structure and can provide a reference for the structural design of high-speed train body.