The wind farm output power fluctuations caused by changing wind speed can be improved by configuring the appropriate storage energy capacity .For the problem that how to select the storage capacity more economical, two indicators for the judgment of the optimization wind power output are mentioned, which is based on a method calculating storage energy capacity. By detailed analysis of the all kinds of factors that can influence the reasonable value of storage capacity, and by using the cost of storage capacity and the smoothing effect of wind farm output as assistant criterion, a reasonable storage capacity range is discussed.