Abstract: With the proposal of "carbon neutrality and emission peak" and the strategic goal of establishing a new power system, the traditional units are gradually replaced by the new energy, resulting in a continuous decrease in the inertia level of the power system. There have been more and more serious active power shock events under low inertia situations, which brings about severe challenges to the frequency stability of power systems. Starting from the definition of inertia of the power system, this paper introduces the relevant factors that affect the inertia level. Based on the definition of inertia, the changing trend of the system inertia level is analyzed after a high proportion of new energy is connected to the grid, and the relationship between the inertia level and the frequency stability is analyzed. The three new features brought by the low inertia level to the power system are analyzed: the scarcity of the traditional inertia support resources, the increased difficulty in the inertia evaluation and the multiple frequency regulation resource coordination. Then, the methods and strategies for improving the inertia of the power system are introduced from the perspectives of generation, grid, load, and energy storage. The control strategies of the battery energy storage participating in the frequency regulation are reviewed from different application scenarios, and its advantages and disadvantages are analyzed in detail. Finally, the control strategies for energy storage and the other potential frequency regulation resources to participate in the frequency regulation in the power system under low inertia level are prospected.