In consideration of the diffusion, electric field migration, and binding, a coupling chloride ion migration model was established based on Ficks second law. The model was verified with experimental data. Using the saline soil environment in Nantong City as an example, Comsol Multiphysics software was used to analyze the migration mechanisms of chloride ions in concrete, to simulate the temporal and spatial distributions of chloride ions in concrete, and to examine the chloride resistance of ordinary Portland cement(OPC)concrete and fly ash concrete with different strength grades. The results show that, in the saline soil environment, the OPC concrete structure cannot meet the durability requirements by only improving the concrete strength grade and protective cover thickness. Fly ash concrete can improve the service life of the concrete structure. In the saline soil environment in Nantong City, a reinforced concrete structure should adopt fly ash concrete, and the protective cover thickness of fly ash concrete with strength grades of C30, C40, C50, and C60 should be 55 mm, 50 mm, 45 mm, and 40 mm, respectively, for a service life of 100 years.