Influences of acoustic-structure interaction on the acoustic characteristics of the expansion chamber water muffler have been studied. The acoustic-structure physics module and the acoustic-shell physics module are adopted. The applicability of the methods in the analysis of mufflers involving strong acoustic-structure interactions has been proved. The acoustic characteristics of water mufflers with elastic walls have been discussed using a 1/4 axisymmetric model. The reliability is validated by comparing the results based on 1/4 model and full model. The calculated transmission loss (TL) of thick-wall muffler is close to that of rigid-wall muffler, which verifies the accuracy of numerical simulation. Effects of elastic walls at different locations have been analyzed. It is found that material properties of the solid have important influences on the acoustic characteristics of water mufflers. The acoustic-structure interaction is enhanced with the decrease of wall thickness. The circumferential elastic wall may cause reduction of the passing fr uency and its frequency bandwidth, while increasing to some extent the maximum noise attenuation. The elastic end chamber wall may change the dome behavior of the TL curve in the considered frequency band with anti-resonance peaks and sharp peaks. The anti-resonance peak is related to the (0, n) radial modes of the end chamber wall. The sharp peak is related to non-planar waves caused by the interaction. The short main pipe elastic wall has little effect on the acoustic characteristics of water mufflers. © 2019 Institute of Noise Control Engineering.