Abstract:The Kiaochow Bay subsea tunnel locates at Kulong Mountain between Tuandao in Shinan District and Xuejia Island in Huangdao District. The area where the tunnel entrance lies is surrounded by large area of seawater. The content of chloride ion in the air near the air-inlet and the entrance of the tunnel is high. Therefore,the areas where the air-inlet and the entrance of the tunnel stand belong to the severe salt mist areas. The monthly average temperature in Qingdao recently is 0 ℃–24 ℃. There are about 90 days in a year when the lowest temperature is below zero. So the lining concrete close to the exits will suffer freeze-thaw cycles. The lining concrete in the tunnel tends to be fractured due to wet-dry cycles. The monthly average relative humidity in Qingdao is between 62% and 86%. So the concrete carbonation takes place faster. Under common transportation and ventilation conditions,the content of CO2 in the air in the tunnel or close to the exits is at least five times of that in atmosphere,where concrete carbonation needs to be considered. ,K+ and Na+ in seawater or underground water can lead to concrete sulphate corrosion and alkali-aggregate action. Therefore,alkali-aggregate action,chloride ion penetration,sulphate corrosion,carbonation,freeze-thaw,fire,and so on should be taken into occount in the durability design of the tunnel lining concrete. It should be stricted on the raw materials of concrete,mixture,properties,quality control,structure design,workmanship,and inspection standards. Furthermore,as the tunnel is an emportant project with 100 years service life,other measures such as concrete surface treatment and imbedded durability monitoring system should be considered. Experiment results show that the carbonation depth of concrete decreases with its increasing compressive strength;and the carbonation resistance capacity of concrete improves with increasing of cement amount and decreasing of w/b. Relationship between chloride ion diffusion coefficient and compressive strength is accordance with exponential function;and the chloride ion diffusion coefficient of concrete would be less than 4×10-12 m2/s when the concrete strength grade is higher than C50.