Abstract: AC excitation variable speed technology is the most widely used and mature technology of variable speed pumped storage, and is the key technology that China needs to focus on in the next step of pumped storage development. At present, the domestic research and development of AC excitation variable speed pumped storage technology is still in its infancy, and there is an urgent need for breakthroughs in all aspects, from the motor structure design, the frequency conversion system design to the machine-network coordinated control strategy. In order to further conquer the key technology of AC excitation variable speed pumped storage and clarify the research and development focus, this paper starts from the basic principle of pumped storage technology, summarizes the characteristics and application conditions of different researching directions of pumped storage technology. Then, the technical characteristics of AC excitation variable speed pumped storage units are emphatically analyzed, and the research framework and focus of the core components of the AC excitation variable speed generator, like the motor, the pump-turbine, the frequency converter and others, are proposed. Finally, the paper gives the overall thinking and methodology of the research on the localization of AC excitation variable speed pumped storage units.