Abstract: Concrete structures located near sea may exhibit bad durability, due to exposing to unfavorable atmosphere, such as high content of chloride ion and fluctuating humidity, for a long time. Thus heavier steel corrosion with cracking and spalling may occur in the design working life, which makes the serviceability and safety worse. Investigations and test to realistic concrete structures have been made, and the damage mechanism and its influencing coefficients of concrete structures under unfavorable atmosphere have been analyzed.The rehabilitation methodology and its effects on the durability of concrete structures have been discussed.Suggestions on rehabilitation and protection of concrete structures exposed to chloride ion and fluctuating humidity are made.