This paper presents experimental research and analysis on packed bed heat storage units for compressed air energy storage systems. We carried out experiments of heat storage cycle in packed beds at different pressures, measured the temperature distribution in packed beds and the variation of air inlet and outlet temperature with time. We also analyzed the heat storage characteristics and efficiency under different pressures. In the experiments we demonstrated the feasibility of multi-stage heat storage in packed beds for compressed air energy storage systems, and proposed approaches for further performance improvement.