Unlike onshore wind farms，the harsh weather conditions（wind and waves）have greater impacts on the offshore wind farm operation and maintenance（O&M）.Taking fully into account of the influence of offshore weather conditions，the paper classifies the O&M strategies of offshore wind turbines into several categories by the components and their respective repair time required by auxiliary equipment.Based on this classification，a new method of availability evaluation of wind turbines with different offshore conditions is presented.A case study demonstrates that the proposed approach can deal with various offshore conditions and O&M strategies.The sensitivity analysis shows the significance of such strategies on the offshore wind O&M availability as an effective technical support.