Wind power is one of the cleanest and safest of all the renewable commercial methods of generating electricity. However, wind energy is difficult to use due to its stochastic variability. Energy storage can overcome the main drawback, allowing energy production to match energy demand. In this paper a new method is proposed to determine the Energy-storage Capacity in Grid-connected Wind Farm. Based on characteristic function of wind power output in wind farm, the method designs the minimum required storage capacity of the wind farm and realizes the stable output and the scheduling of wind farm. The results of this paper demonstrate the leading role of a well-optimized design for technical and economic viability of such systems.