With the capacity of single wind turbine and the size of wind farm increasing,the reliability issues of grid-connected wind farms become increasingly prominent. Compared with conventional power supply,wind power has strong stochastic volatility. Then the reliability evaluation indices for conventional supply don’t apply to wind power. So it is more and more important to research and development the evaluation indices for the reliability of wind power. On the basis of the analysis to factors affecting the wind reliability,for indices are defined,which are wind farm capacity validity coefficient(CVC) ,wind farm generation intensity coefficient(GIC) ,wind farm operation security coefficient(OSC) ,wind farm relative benefit coefficient. They evaluate the reliability of wind power generation from point of abundance,continuity,security and economic. Addition,this paper proposes defined formula for each index. All these indices can be used to indicate the economy and substantial value of wind power,and are helpful for the planning and operation of gird-connected wind farm.