Structural health monitoring is essential for ensuring the structural safety performance during the service life. The process is of paramount importance in case of the floating wind turbine due to the structural parts subjected to the marine environmental risky conditions. In this paper a fuzzy-based damage identification method using dynamic response of the Spar floating wind turbine has been proposed. In the first step, the nonlinear equations of motion of the floating wind turbine system derived using the theorem of conservation of angular momentum and Newton’s second law. Then the variation values of the frequency characteristics of the structure in each DOFs due to stiffness changes of mooring lines (simulated damage) are considered as input features to the fuzzy system. Also the fuzzy system was trained based on calibrating of the membership functions by defining the damage classes properly. For validating the proposed method, noise with different SNRs was contaminated to the measured features and the success rate of the damage detection was calculated. The results showed that the proposed method is able to identify the damage classes with acceptable success rate.