Xiamen Xiangan Subsea Tunnel is the first undersea tunnel constructed in China.It has become the major undersea pathway connecting Xiamen Island and Xiangan District since its operation in 2010.The total length is 6.05 km with the undersea length of 4.2 km.In an effort to onsite-monitor reinforcement corrosion in concrete structures,the commercially available CorroWatch multiprobe sensors and ERE-20 reference electrodes were pre-embedded in the selected locations and positions of supporting structures during the tunnel constructions.The real-time data have been collected annually by onsite measurements for 6 years.In this paper,the feasibility of the onsite corrosion monitoring system and suitability of the measured parameters including corrosion current,potential and temperature are discussed based on the preliminary results.The measured typical cyclic-type variations in corrosion current and temperature with monitoring time might be related to the seasonal changes during the annual routine measurements.The widely scattered corrosion potentials that are fluctuated complicatedly reflected localized differences in the vicinity of rebar and concrete.These findings,along with the progressively ongoing research,will provide valuable information in structural durability for service life prediction of reinforced concrete structures exposed to marine environments.