Abstract: The monopile offshore wind turbine (MOWT) structure is subjected to coupling damage caused by chloride corrosion and wind-wave fatigue over long-term service period, resulting in the gradual degradation of its hazard resistance throughout its life cycle. Moreover, MOWTs are mostly highly flexible, thin-walled structures that are very sensitive to local defects. When a local defect is large, overall instability driven by local buckling often occurs. Under these conditions, the structural failure also is highly sudden and significantly reduces the safety reserve. Corrosion-fatigue coupling damage, as a local defect that gradually forms and propagates during service, leads to a progressive increase in the risk of local buckling, causing the structure failure mode to evolve continuously over time. Most existing studies on the life-cycle hazard resistance of such structures ignore this coupling effect, rendering them unable to effectively identify time-varying failure modes. Furthermore, existing performance quantification indices are only suitable for a single failure mode, resulting in a large deviation in life-cycle failure risk assessments. To address these issues, based on the interactive coupling damage calculation theory of multi-environmental factors, this paper considers the influence of corrosion-fatigue coupling effect and its uncertainty on structural failure mode, and proposes an efficient failure mode discrimination method using the fuzzy transformation principle and membership degree theory. On this basis, a time-series multi-index performance evaluation model is further proposed to analyze the life-cycle hazard resistance performance of the structure. Finally, taking a 5 MW MOWT as an example, the influence of multiple strong typhoons and earthquakes on the cumulative failure risk of the structure is analyzed. The results show that the collapse probabilities obtained from three randomly generated hazard sequences are 3.40%, 27.10%, and 7.48%, respectively, demonstrating the necessity of employing Monte Carlo simulation to account for the randomness of hazard occurrence. Based on this approach, the probability of buckling-induced collapse under multi-hazard scenarios is estimated to be approximately 13.26% when the effects of long-term corrosion-fatigue damage are considered. In contrast, the collapse probability decreases to 7.49% when the coupled damage effect is neglected, further highlighting the significant influence of damage-induced defects on structural performance assessment. Finally, to validate the accuracy of the proposed evaluation method, comparisons with an actual engineering case were conducted; the results indicate that the relative error between the predicted and observed results is only 13.44%.