Nowadays, the service life monitoring of mooring lines attracts more and more attention from the marine renewable energy (MRE) industry where developers desire to have a closer look on the safety margin. Besides, current standards are also being improved in order to ensure safe and cost-effective design for MRE devices. In the present study, we believe that monitoring and modeling should be implemented in parallel in order to better estimate the actual state and the reliability of the system during the expected service life. Besides, it is crucial to clarify the mechanic of the mooring line responses, to understand why and how they are modified during deployment, and how those can be accounted for in order to update the actual fatigue damage and predict the remaining allowable service life of system. A comprehensive modeling and service life monitoring methodology for mooring lines of floating wind turbines (FWTs) is discussed by the authors based on the reliability approach. Critical factors that influence structural behaviors such as material deterioration and marine environmental factors involved are identified and accounted for in this reliability-monitoring basis. Ultimately, based on the reliability level estimated, decisions regarding required maintenance or replacement of lines can be made.