The study on the economic dispatch provides an efficient solution for the large-scale wind power grid-connected system operation.Due to the limited accuracy of wind power forecasting，a wind power prediction credibility model is built. And a wind power forecasting error model is proposed by use of partition modelling method.Based on those models，the energy storage cost considering forecasting credibility is discussed.Combining with thermal units cost，an economic dispatch model of power system with wind farms is completed.The model considers the probability of loss of load and curtailed wind power.In order to reduce the energy storage cost，the energy storage capacity is showed as the probability of wind power forecasting error.Simultaneously，the energy storage cost adjustment factor is added into the objective function，which is used in the decision making of wind power dispatch.Taking a10-machine system as an example，the feasibility of the proposed method is verified through Monte Carlo simulation technology and fuzzy clustering method.