A reliability-based quantitative durability design methodology is presented for reinforced concrete ( RC) structures in the marine environment on the basis of natural exposure data derived from four berths (1.5, 1.5, 4 and 15 years) of a concrete port. More than 200 chloride profiles are obtained and analyzed. The relationship between nominal surface chloride ion concentration and altitude is discussed. Subsequently, the formula of the apparent chloride diffusion coefficient is proposed with consideration of the surrounding temperature, sodium chloride solution concentration, age factor and altitude. Then, the reliability-based method to predict the durability of RC structures is developed according to Fick's second law. Relationships between the predicted penetration depth of the chloride ion, the ratio of the wetting time per-period and the corresponding altitude are discussed. Subsequently, the environmental zonation methodology is established for concrete structures under a marine chloride environment by considering the ratio of the wetting time per-period of concrete as the zoning index. Finally, the corres-ponding durability design method for each zone level is established, which contains the durability design regulations of the specimen, and correction coefficients for different water/binder ratios, ages, temperatures and chloride ion concentrations.