Offshore wind turbines are exposed to long-lasting harsh marine environments with high humidity and salt spray. With an increase in service time, accidents such as corrosion fatigue of basic steel pipes and fan collapse, can occur. Therefore, it is important to monitor the corrosion of steel piles. In this study, the application of distributed optical fiber sensing technology to the corrosion monitoring of steel piles is explored in a simulated marine environment. By wrapping distributed optical fibers around the surface of the steel piles, the strain changes in the steel piles due to corrosion products in the atmospheric zone, water level fluctuation zone, and immersion zone are monitored. Based on this, a relationship between the circumferential strain and mass loss of the steel pile is established. The corrosion areas of the steel piles are visualized using color cloud images. The research results show that distributed optical fiber sensing technology can be used for the online monitoring of steel pile surface corrosion and can locate the corrosion area and quantify the degree of corrosion, which provides technical support and assurance for the early warning and maintenance of offshore wind turbine steel structures.