In nuclear power plants, the amount of spent fuel stored on-site is limited. Therefore, it is necessary to be shipped to off-site storage or disposal facilities regularly. The key risk in the transfer of spent fuel involves a release of radiation that could cause harmful effects to people and the environment. Transfer casks with impact limiters on both ends are always employed to ensure safe containment of radioactive materials, which should be verified by the 9 meters drop test onto an unyielding surface according to IAEA SSR-6. In this paper, we focus on the influence of the impact-limiter parameters, including geometry dimensions and mechanical properties, on the results of drop events to achieve an optimized approach for design. The typical structure of impact limiter is bulk energy-absorbed material wrapped by thin stainless-steel shells. Compared to traditional wood, foam has advantages of isotropy and steady quality. In this paper, theoretical and numerical methods are both adopted to investigate the influence of impact limiters during hypothetical accidental conditions for optimizing buffer influence and protecting the internal fuel components. First of all, a series of polyurethane foam is selected according to the theoretical method, because its mechanical property is related to density. Therefore, using explicit finite element method to investigate the influence of parameters of foam in impact limiter. These discrete points from the above result can be utilized to establish damage curves by date fitting. Finally, a design approach for spent fuel transfer cask is summarized, to provide a convenient formula to predict the damage and optimize structure design in drop condition. Furthermore, this design approach can be applied in the multi-module shared system of SNF, which can contain different fuel assemblies.