The traditional liquid cooling system of containerized battery energy storage power stations does not effectively utilize natural cold sources and has the risk of leakage. To address the above problems, a novel two-phase liquid cooling system with three operating modes was developed. An annual field test was carried out for containerized battery energy storage power stations. The thermal management performance and energy-saving effects under continuous charging and discharging conditions are analyzed by examining the main influencing factors of battery temperature and cooling system characteristics (battery temperature variation, temperature uniformity, supply liquid temperature, and annual energy consumption). The operating condition of the fluorine pump was analyzed. The results showed that the cooling system can control the maximum temperature difference of 4°C during continuous charging and discharging in different weather conditions, and the maximum EER annually reaches 14.2. Compared to mechanical cooling, thermosyphon loop cooling achieves maximum energy savings of 13.5% with a supply liquid temperature of 25~28°C. During the spring transition season at 20°C, the system can still be cycled through thermosyphon loop cooling, with the fan continually running to maintain the supply liquid temperature at 24°C, which is 41% more energy-saving than hybrid cooling. The rotational speed of 60% with the frequency of 36HZ is recommended due to the equipment's relative stability for long-term running. These results show that this novel system can effectively make full use of the natural cold source for energy-saving and utilizing a two-phase liquid cooling to maintain temperature uniformity even in continuous charging and discharging conditions and high-temperature weather for containerized battery energy storage power stations.