Abstract: A double-plate structure with elastic connection,in which two parallel rigid plates are supported by an elastic connecting element,is developed to achieve underwater broadband sound insulation.Using the method of vibration analysis of spring vibrator and the theory of sound propagation,the sound insulation theoretical model under the plane wave incidence is developed,and the influences of structure parameters on the sound insulation is analyzed.The sound transmission loss will increase consistently by reducing the elastic coefficient per unit area sufficiently or increasing the mass per unit area of the end plate sufficiently.Through the finite element simulation,the vibration displacement and acoustic input impedance of the double-plate structure are analyzed,and the sound insulation characteristics of the double-plate structure and the continuous media layer,such as the uniform elastic layer and the elastic layer with cavities,are compared.The results show that reducing the mass of elastic element is helpful to eliminate the half-wavelength full transmission phenomenon at low frequency.Compared with the continuous media layer with the same thickness,quality and static compression ratio,the double-plate structure with elastic connection can reduce the vibration and sound coupling of the bilateral fluid more effectively,and have better sound insulation performance with wider bandwidth,better in-band consistency and larger sound transmission loss.