Power injection becomes stochastic due to large-scale wind power integration into power system, which has a serious impact on the safe and economic operation of traditional power system. The uncertainty of wind power has a significant impact on power system economic dispatch. To deal with this issue, based on interval number theory, the concept of dynamic cost of wind power and the optimization model of power system interval economic dispatch incorporating dynamic wind power cost are proposed. Decision variable is introduced to achieve the interval optimization, the value of which can reflect the operation risk and economic benefit of power system and provide decision support for system operators to a certain extent. An IEEE 30 bus test system is adopted to verify the practicality and effectiveness of the model and method.