Abstract: In order to measure the radiated noise of underwater structures accurately and quickly, a marine reverberation pool needs to be built based on harbors or coasts. For the sound insulation problem of the wall of the marine reverberation pool when the inside and outside are all water, air-filled sandwich plates with beams are designed, and the sound insulation performance of such plates with different parameters is compared through simulations. In order to evaluate the sound insulation performance of underwater large-scale sound insulation structures under the condition of random incidence of sound waves, the reverberation evaluation method is proposed. The difference between the reverberation method and the impulse method is compared by the sound insulation experiment. The results show that the proposed underwater sound insulation structure has excellent sound insulation performance, in the case of random incidence, the insertion loss of a 0.015 m–0.02 m–0.015 m air-filled sandwich plate with beams in the frequency range of 2−10 kHz exceeds 20 dB. The reverberation method can effectively evaluate the average sound insulation performance of large-scale underwater sound insulation structures. And the measured average sound insulation performance for random incidence of sound wave is suited to the actual application.