Abstract: When Energy storage system, which has such characteristics as quick response and accurate tracking, is applied in primary frequency regulation of regional power grid, the transient frequency characteristics will be improved effectively. In order to coordinate energy storage system and conventional thermal units, such issues as the primary frequency regulation characteristics of conventional thermal units and its cooperation with energy storage system and their coordination operation are analyzed based on the primary frequency regulation mathematical model of regional power grid. The coordination principle that conventional thermal units take main role and the energy storage system takes the supplementary role in primary frequency regulation is proposed. In addition, the whole control strategy of primary frequency regulation with the involving of energy storage system, which includes such functions as improved droop control, exiting control of regulation control and energy management control, is proposed. In the end, its effectiveness is verified through the simulation results.