To investigate the chloride ion transport law in saturated concrete, a meso-scale model for concrete that considering different concrete mixtures with cement paste, aggregate and interfacial transition zones is established. Through the established model, the chloride ions concentrations are calculated in one-dimensional and two-dimensional diffusion, respectively. The simulation results are used to compare with the experimental results. The effects of water-cement ratio and degree of hydration on chloride ion diffusion are analyzed and the initial corrosion time of steel reinforcement in reinforced concrete structures is predicted in coastal environments. The comparison results show that when calculating in the meso-scale model for chloride ion diffusion, it is important to consider the interfacial transition zone, with a thickness of 80 μm. The calculated values of the meso-scale model of chloride ion concentration diffusion are in good agreement with the experimental results. . In a chloride-rich environment, the initial corrosion point on the surface of steel reinforcement is not fixed. Under the same conditions, the initial corrosion time of steel reinforcement in one-dimensional diffusion of chloride ions is 2.31-3.24 times that of two-dimensional diffusion. when the thickness of the protective layer is increased from 50 mm to 60 mm and water/cement ratios are 0.4, 0.5, and 0.6, the initial corrosion time of steel is extends by 28.00%, 10.90%, and 18.50% in one-dimensional diffusion and is extended by 52.42%, 7.45% and 56.65% in two-dimensional diffusion, respectively. The results in this study can be useful for predicting the initial corrosion time of steel reinforcement in coastal environments.