The invention discloses a compressed air energy-storage power generation system and a working mode thereof. The compressed air energy-storage power generation system comprises a compressed air storage device, as well as an energy charge unit and an energy release unit which are connected with the compressed air storage device, wherein the energy charge unit comprises a plurality of stages of serially connected air compressors, and a primary heat accumulation tank and a primary cooler which are connected in series are sequentially arranged close to the outlet of each stage of the air compressors; and the energy release unit comprises a heat accumulation tank, a plurality of stages of serially connected turbines and a regenerator arranged behind the final-stage turbine, and except for the final-stage turbine which is a gas turbine, others are all air turbines. The compressed air energy storage power generation system further comprises a bypass crossing over the outlet of the regenerator and the outlets of all the stages of air turbines. The invention also discloses a working mode of the compressed air energy storage power generation system. Compared with a conventional compressed air energy-storage system, the compressed air energy-storage power generation system is larger in energy density, higher in output power, relatively high in efficiency and suitable for large-scale intake of off-peak electric energy, or wind power, photo-electricity and other unstable renewable energy resources, thereby realizing load shifting of a grid and stable grid connection of the renewable energy resources and acquiring substantial economic benefits.