All of electrical equipment in wind farms，such as transformer and switchgear，need regular maintenance or pre － test，and then the wind turbines which connect with the electrical equipment have to stop． Considering the failure probability and maintenance opportunity of the main components of electrical equipment and wind turbines in wind farms，a preventive opportunistic maintenance strategy is proposed for wind farms based on reliability． On the basis of preventive maintenance of electrical equipment in wind farm，the strategy implements opportunistic maintenance for key components of the wind turbine which directly connects with the electrical equipment which need to be repaired． When the reliability of electrical equipment reduces to the preventive threshold，the preventive maintenance is implemented． Then，the reliability of components of the wind turbines which connect with the repaired equipment directly is checked． If the opportunity threshold is larger than the reliability，the opportunistic maintenance is implemented． Through the optimization of the preventive threshold and opportunity threshold，the power loss and maintenance cost of wind farm are minimized． Finally，the wind farm system is simulated to verify the effectiveness of the proposed strategy，which can reduce the repeated outage time of wind turbines，and provide a new means for the intelligent maintenance of wind farms