Abstract: Based on the low-frequency broadband sound absorption characteristics of underwater resonant cavities and building upon traditional acoustic materials, this paper employs elastic films to alter the modal sound field characteristics inside the cavity. By analyzing changes in parameters such as the material, thickness, and number of layers of the films, as well as the influence of additional mass blocks on transmission loss, a combined model consisting of a multi-mode elastic resonant cavity array and an acoustic covering layer is designed. Test results of the model specimens show that, compared with traditional noise reduction structures, the multi-mode elastic resonant cavity array combination device achieves a sound absorption coefficient greater than 0.8 near 800 Hz and demonstrates superior sound absorption performance in the low-frequency band below 1 kHz.