To deal with the stable operation of multiple energy storage power stations participating in primary frequency regulation, a cooperative frequency regulation control strategy for energy storage power stations was proposed with the consideration of the State of Charge (SOC) equilibrium demand. Firstly, the frequency regulation control model of regional power grid with multiple energy storage power stations is established, and the basic control principle of energy storage power station participating in primary frequency regulation is analyzed. Secondly, based on the net power variation within the action zone and dead zone of frequency regulation, different frequency band power and coupling complementary characteristics of SOC balance power are analyzed. The feasibility of the energy storage SOC balanced control and coordinated control of frequency regulation demand is demonstrated, and frequency regulation is obtained on the basis of the design on the coordination of energy storage frequency regulation control strategy. The design method of key control parameters is given. The proposed method not only realizes the frequency regulation, but also reduces the SOC out-of-limit risk and enhances the frequency support effect. Finally, a typical regional power grid model is built and simulated with different frequency fluctuation conditions. The results show that the proposed control strategy can effectively improve the frequency quality and achieve the balance of the charged state of multiple energy storage stations without increasing the frequency regulation burden of the system.