Abstract: A study of sound insulation capability of underwater elastomers containing cavities has been made.By using the Kelvin-Voigt viscoelastic model,the dynamic equivalent bulk modulus,the effective shear modulus and the equivalent dilatational wave speed of the material are deduced.The insulation ability of the equivalent material and the equivalent sound speed has also been calculated by transfer matrix theory under different porosity and cavity radius.The results of simulation show that cavity radius and porosity affect the sound insulation capability of composites,and the conclusion is useful for the design of sound insulation materials.