The study on the penetration of chloride ions into concrete is very important for the durability assessment and design of reinforced concrete structures. A cyclic wetting and drying test is conducted to evaluate the effects of concrete mix proportions on the penetration of chloride ions. Based on the experimental results, the variations in chloride ion content at various points in concrete with the water/cement ratio, maximum aggregate diameter, aggregate gradation, fly ash content, and anticorrosion agent content are analyzed quantitatively. It is found that the water/cement ratio, aggregate gradation, maximum aggregate diameter, and fly ash all have a larger influence on the penetration of chloride ions. These conclusions can provide theoretical evidence for the design optimization of concrete properties.