Abstract: In this paper, the acoustic characteristics of the seawater muffler with waterproof and sound absorption layer covered inside are computed, thus the numerical simulation method is established to handle such problems. First, based on the layered-media theory, the acoustic characteristics of the waterproof layer with cavity are analyzed, the three-dimensional finite element model of the seawater muffler is built up by using ANSYS. T hen the acoustic pressure distribution and translation loss of the seawater muffler is obtained in SYSNOISE with the sound absorption coefficient and surface impedance of the waterproof and sound absorption layer as th e boundary condition. The acoustic characteristics of the seawater muffler are analyzed and calculated. The results can be useful to improve the noise reduction effort of seawater mufflers with waterproof and sound abs orption treatment.