There are several challenges toward maintaining offshore wind turbines such as ensuring the intrinsic performance of the wind turbine, maximizing short- and long-term profits, and optimizing maintenance grouping. These criteria should be optimized in respect to several practical constraints. Moreover, issues such as decision-making in uncertain environments where reliability-oriented field data are insufficient and information regarding the state of health state also be tackled.This paper proposes a failure model that includes multiple failure modes with different failure consequences. Logistic delays and weather conditions are also obstacles for performing maintenance activities. To save logistic cost and downtime loss, a two-level maintenance policy considering both periodic maintenance planning and reactive maintenance is developed. The first level is aimed at failure modes whose degradation process is black-box by grouping individual maintenance activities according to their own maintenance period. The second level is aimed at those failure modes whose failure can be indicated through two options: 1) Integration with existing maintenance tasks of the first level and 2) creating a new maintenance opportunity. The effects of decision thresholds on the choice of maintenance options are studied through simulations.