With the capacity increasing of single wind turbine and the size of wind farm, the generation reliability issues of wind farms become increasingly prominent. Compared with conventional power supply, wind power has strong stochastic volatility. Then the reliability evaluation indices for conventional supply are not suit for 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, four 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 (RBC). 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. More importantly, the paper gives operator example which indicates the four indicators as an evaluation system is feasible. The results are qualitative evidence, which demonstrates that compared with conventional power, wind power reliability is low as a power supply. They can be quantitative characterization of difference between wind farm and wind farm, as well as the operation status of a single wind farm. 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 grid-connected wind farm.