Abstract: For the problem in the safety assurance for long-term maritime storage of spent fuel for marine nuclear power platform, this paper improved the fixed form between the fuel assembly and the storage cell, optimized the connection form between the storage cell and the spent fuel storage grid frame body, and added a buffer structure between the spent fuel storage grid and the wall of the spent fuel pool. In this way, a spent fuel storage grid meeting the design criteria and adapting to the marine environment is designed. Monte Carlo code MCNP-5, computational fluid dynamics (CFD) software Fluent 14.0 and finite element analysis software ANSYS 17.0 are used to simulate the criticality, the thermal hydraulics and the structural of this storage grid. The results show that the design of the storage grid is reasonable and safe. Therefore, the spent fuel storage grid designed in this study can provide a solution for the maritime storage of spent fuel in floating nuclear power plants.