With the aim of carbon peak and carbon neutrality, the integration of high-proportion renewable energy sources (RESs) makes the low-inertia characteristic of the new power system more obvious. In order to ensure power system security and stability, and support the integration of RESs, the research on the power system inertia was reviewed and prospected. The essence of the power system inertia was introduced, and the correlation among the conventional inertia, virtual inertia and equivalent inertia was discussed, on which the physical significance of the virtual inertia was revealed. From the viewpoints of the sources of inertia, the research on the virtual inertia control of the wind machine, photovoltaic generation, and energy storage system was summarized. Additionally, the assessment methods of power system inertia were reviewed. The important issues to be focused in the research area of power system inertia were summarized, and the suggestions for further studies were provided.