High penetration of wind power is a prominent feature of novel power system, while the randomness and anti- peak shaving of wind power lead to a greater demand for flexibility. Energy storage system（ESS）can effectively improve power system flexibility to cope with wind power uncertainty.Analyzing the impact of ESS on system flexibility is conducive to ESS planning and utilization. Based on the source- load-storage interactive economic dispatch model, considering the participation of ESS in system peak regulation, climbing and spinning reserve, the wind power dispatchable region is calculated by iterative generation of off- limit constraint boundary. The contribution of ESS to system regulation ability was quantified by comparing the positive and negative deviation boundary of system wind power dispatchable region under different ESS capacities and locations. IEEE 30-node system case study analyzes the influence of the distribution and capacity proportion between ESS and other flexible resources on system flexibility improvement, which provides decision supports for configuring ESS participating in power grid dispatching.