Underwater sound-absorbing structures typically utilize viscoelastic materials, such as rubber and polyurethane, as substrates to match background medium impedance and induce sound energy dissipation. However, at operating depths ranging from tens to hundreds of meters, hydrostatic pressure acting on these materials alters their mechanical properties, causing significant deviations in surface acoustic impedance compared to ambient pressure conditions. This compromises performance predictions for subsea acoustics in practical environments. This paper develops an analytical acoustic impedance model for metasurfaces using the transfer matrix method and equivalent medium theory. By integrating pressure-induced dynamic variations in mechanical properties, it computationally predicts the sound absorption spectrum at 2 MPa hydrostatic pressure. Controlled experiments compare the absorption spectra under pressurized and ambient conditions, thereby validating the theoretical framework. The proposed methodology provides a novel approach for modulating and predicting acoustic impedance of functional materials across varying underwater depths.