Abstract: Taking horn cavity as an example, the rule of sound propagation in cavity was researched, and the amended calculation method taking account of energy dissipation in the cavity was summed up. The validity of calculation method was also verified through sound pulse pipe test. Furthermore, the vibration and self-noise distribution of sonar platform was predicted through numerical experiment. The influence of cavity wedge laying conditions to sonar platform acoustic characteristics was analyzed. The results show that the cavity acoustic energy absorption is very effective in low frequency, and the calculation of cavity wedge acoustic performance must be taken into account below 3kHz.The laying of cavity wedge obviously reduces the vibration level and total self-noise level of sonar platform, part laying method of wedge must consider the pressure distribution of sonar array.