Abstract: A corrosion monitoring system for offshore wind turbines was developed using resistance probe sensors (TER) and installed in an offshore wind power project in Zhanjiang, Guangdong Province, in the South China Sea. The internal and external corrosion rates and corrosion environment levels of the offshore wind turbines in the project were evaluated based on the monitoring results. The results show that the internal and external corrosion environment of offshore wind turbines were typical marine atmospheric corrosion environment, showing obvious wet-dry rotation. The maximum corrosion rate of external and internal corrosion appeared at the primal phase, and gradually decreased with the extension of service time and finally tended to be stable. The power function model of corrosion volume and time was obtained by fitting the data. Finally, some suggestions on the design grade and durability requirements for offshore wind turbines were proposed.