Bubbling deaeration is widely applied in marine steam power system (MSPS), and direct contact condensation (DCC) of steam injected into water under low subcooled water is the thermodynamic foundation of this technology. Due to the small delta-T below saturation of the flow field, the steam condensation potential is small, and there is a violent steam plume evolution. The process and the growth, merging, breaking and collapse of bubbles, which produce severe pressure oscillation and vibration noise. In response to this problem, the flow pattern evolution and acoustic characteristics of underwater steam injection in the range of different subcooling degrees (10–0.2°C) and steam mass flow (18kg/h) were studied through experiments. Studies have found that the degree of subcooling has an important impact on the evolution of the steam plume and the spectral characteristics of noise. The change in the shape of the steam plume determines the amplitude and spectral characteristics of the noise sound pressure. As the ambient water temperature rises, the steam plume shape changes differently, and the phenomena such as “tail oscillation”, “congestion”, and “steam recirculation” appear in sequence. Affected by the evolution of the above-mentioned steam plume shape, the noise sound pressure amplitude changes with the subcooling. The temperature first rises and then falls, and it rises slightly when it is close to the saturation temperature. At the same time, the noise spectrum shifts from medium and low frequency to low frequency. When it is close to the saturation temperature, the spectrum tends to move to medium frequency.