In order to efficiently use Energy Storage System (ESS) to meet the Primary Frequency Regulation (PFR) needs of the power grid, a control strategy for ESS based on dynamic droop coefficient and dynamic SOC reference is proposed. It is proposed to divide the ESS frequency regulation process into frequency regulation stage and SOC recovery stage with the frequency dead zone of power system as the boundary. In the frequency regulation stage, the SOC and the maximum frequency deviation are used as control variables to adaptively adjust the output of ESS to prevent the SOC from exceeding the limit. In the SOC recovery stage, first, the dynamic SOC restoration reference adjustment method that adapts to load changes is proposed. Then, a method for determining the output power of ESS that takes into account the SOC recovery requirement and the power grid affordability is proposed. Finally, a double-layer fuzzy controller is designed to determine the dynamic SOC restoration reference and the power of the ESS. Three evaluation indicators are proposed to evaluate the frequency regulation effect and SOC maintenance effect. Taking a certain regional power grid as an example, the effectiveness of the proposed strategy is verified under step load disturbance and continuous load disturbance. The simulation result shows that the SOC maintenance effect and frequency regulation effect of the proposed strategy is 9% and 4% higher than the comparison strategy, respectively. This work is supported by the Central Government Guiding the Basic Research Project of the Provincial Key Laboratory of Local Science and Technology Development Funds (No. 202002005JC) and the Science and Technology Project of Huayun Clean Energy Co., Ltd. (No. 2020220202000042).