Graphene is becoming more and more significantly applied as anti-corrosion coating in marine environment. However, graphene could suffer from destruction to cause failure by the diffusion dynamics of O atom. Therefore, it should be of significance to understand the diffusion processes of O atom on graphene in marine environment. Through the first-principles calculations, it was found that the Cl atoms contained in the surrounding environment could adsorb on graphene, and the differential charge densities indicated that the CCl bond was coordinated by ionic bonds and covalent bonds. The band structure and density of states revealed that the adsorbed Cl atoms could destroy the integrity of the sp2 structure of graphene, which caused to greatly increase the diffusion rate of O atom. The adsorption energies of O and Cl on graphene were analyzed, showing that Cl atoms promote the adsorption of O atom. Fortunately, fluorinated graphene could increase the diffusion energy barrier of O atom, which would be effective for the protection of oxidative corrosion of graphene in marine environment. These results provide a theoretical basis for the application of fluorinated graphene as a potential anticorrosion material in the ocean or coast.