Abstract: Through the combination of hollow blocking mass with polyurethane sandwich plate, the composite low-noise brace structure is designed. Its preliminary marine application is also presented. On this basis, the large scale double shells’ underwater model test of vibration, sound radiation and input power flow is carried out. The test data show that the outer shell 20Hz-3000Hz vibration acceleration level is reduced by 3.1dB, the near field sound radiation pressure at 5m is reduced by 7.2dB. The 90°-270° clockwise circumferential distribution of sound pressure has the highest noise reduction. The input power flow is also obviously attenuated, which is single-peaked and moves to lower frequency.