The underwater acoustic radiation of air cushion vehicles (ACVs) is a complex process considering hull structure-aircushion-water three-phase interaction and vibro-acoustic coupling, which has complex transmission characteristics and is the key and difficult issue in the ACV acoustic analysis. With an ACV taken as a computational example, the vibro-acoustic finite element method (FEM) and the analytical method were used to analyze the transmission characteristics of the underwater radiation noise of the ACV. To calculate the underwater acoustic field for mechanical noise sources and airborne sources of lift fans, a vibro-acoustic FEM numerical model considering structure-air-water interaction was established and calibrated by the natural frequency of the hull obtained from the tests. The analytical formulas were used to calculate the underwater acoustic field for airborne sources of other equipment. The overall sound pressure level (OASPL) at points 1 m from the port and starboard sides was adopted as an evaluation index. The research shows that the underwater radiation noise of the ACV is broadband noise. The underwater acoustic pressure calculated by the FEM increases with the increase of frequency, and the pressure is concentrated on the aircushion-water interaction surface at low frequencies. With the increase of frequency, the underwater acoustic field calculated by the FEM gradually presents an irregular interference distribution. The underwater radiation noise caused by the acoustic excitation of equipment like air propellers is mainly near-field and low-frequency noise, accounting averagely for 40% of that of the ACV within the sound radiation range of the equipment. The transmission characteristics of underwater radiation noise of ACVs revealed in this paper has important guiding significance for the vibration and noise reduction of ACVs.