This paper presents a simulation method that can assess the impact of energy storage system（ESS） on the unit commitment（UC） problem with volatile wind power. In order to achieve the higher system flexibility and reduce the impact of volatility of wind power， ESS is incorporated into the UC problem with wind power. The UC problem with wind power and ESS is formulated as the mixed-integer convex program， which is optimized by branch and bound combined with interior point method. During the branch and bound process， best first search and depth first search are combined to expedite the computation. Numerical simulations on a ten-unit system show that the introduction of ESS is effective to reduce the impact of volatility of wind power on the UC problem.