A compressed air energy storage system comprises a high-pressure water apparatus, a low-pressure water apparatus coupled to the high-pressure water apparatus through two channels, wherein a first channel is formed by a pumped hydroelectric power generation unit, a first high-pressure pipe and a first low-pressure pipe and a second channel is formed by a gas-water energy exchange unit, a second high-pressure pipe and a second low-pressure pipe and a compressed gas storage unit coupled to the gas-water energy exchange unit.