With the development of Vehicle-to-Grid (V2G) technology and increasing number of electric vehicles (EVs) integrating in power grid, supplementary frequency regulation service provided by V2G aggregator has been seen as the most promising grid ancillary service provided by the integrated EVs. In this paper, an optimal dispatching strategy of V2G aggregator is proposed to satisfy the driving demand of EV owners and maximize the economic benefits of aggregator simultaneously when it participates in supplementary frequency regulation. A judgment module is designed to determine EVs in aggregator whether participating in frequency regulation according to EV battery SOC for EVs' driving demand, which is calculated by EVs' daily driving distance. An optimal regulation power calculation model is built to optimize profits of aggregator and tracking performance of frequency load control signal from grid operator. A fair regulation power allocation module is designed to avoid over-discharging of EVs in aggregator. Finally, the proposed strategy is implemented in the simulation experiments to demonstrate its effectiveness. (C) 2016 Elsevier Ltd. All rights reserved.