This paper analyzes the failure modes of reinforced concrete structures in marine environment, which is mainly influenced by the chloride ion erosion. Under the action of chloride ions, reinforced steel bars are corroded seriously, leading to cracking. We carry out this process in detail, evaluate the amount of corrosion, and then establish a cross-sectional area model of steel corrosion. Based on Fick’s law, the quantified treatment of chloride ion penetration, critical concentration, and diffusion coefficient, etc. are processed. We establish the deterioration model of steel with resistance deterioration, and analyze the reliability of the reinforced concrete structures.