Abstract: The application scenarios and site selection range of compressed air energy storage (CAES) can be effectively expanded through underwater air storage, which provides large-scale, long-term energy storage support for the exploitation of deep-sea and far-offshore wind power resources and the construction of large-scale integrated hydro-wind-solar-storage new energy bases. Firstly, the technical principles and application scenarios of underwater compressed air energy storage were introduced, and the characteristics of constant pressure and complete inflation/deflation of underwater air storage, along with its advantages of high efficiency, flexibility, and safety, were analyzed. Then, an experimental setup utilizing a pressurized water tank was constructed to simulate the underwater environment. The deployment time and energy conversion efficiency of underwater flexible air storage bag were analyzed through experimental tests and theoretical calculations conducted on different water bodies, including seawater, lake water, salt lakes, and reservoirs. Results indicate that, for air storage bag, the deployment time is longer and the energy storage capacity is higher in water bodies with higher density. The energy conversion efficiency during the compression process increases with the rise in water density, the increase in underwater temperature, the decrease in ambient air temperature, and the increase in water depth.