Abstract: Amid the increasing scarcity of terrestrial resources, the vast resource potential of the marine environment has accelerated human exploration and exploitation of the ocean. As a crucial pivot for maritime activities, the construction of underground oil storage facilities on islands and reefs can serve as an energy foundation for various projects. However, the potential risk of oil leaks cannot be overlooked, as oil spills on islands and reefs can contaminate freshwater lenses and even spread further into the ocean, causing significant harm to the ecological environment. To investigate the pollution migration patterns of underground oil storage leaks and their invasion mechanisms into freshwater lenses, This study determined the pollution migration characteristics and primary driving forces through indoor simulation experiments. A numerical model of the same scale was established using COMSOL to further clarify the influence of different rainfall intensities and oil properties on pollution migration. The results indicate that oil pollution migration under the hydrogeological conditions of coral islands and reefs is primarily influenced by two driving forces: vertical migration driven by gravity and seaward discharge driven by the dynamic groundwater flow field on islands and reefs. The stronger the rainfall recharge intensity on islands and reefs, the greater the influence the groundwater flow field on driving pollution seaward, and the less impact on freshwater lenses. DNAPL-type oil pollution exhibits different migration patterns from LNAPL-type oil pollution, but it has no significant impact on freshwater lenses. This study provides a theoretical basis and information for the selection of oil storage sites, pollution prevention, and freshwater resource protection during the development of coral islands and reefs.