An experimental system, including a plexiglass water container and four active vibration isolators, was established to demonstrate the efficiency of active vibration isolation in suppressing structural vibration as well as underwater sound radiation. For this fluid-structure coupled system, finite element analysis and experimental modal testing were conducted to exhibit and validate the vibration modes and radiated sound in the fluid. In the experiment, the fundamental frequency of the rotating disturbance is nearly equal to the first natural frequency of the coupled system, which helps to create a strong sound field in the water by resonant structural vibration. The disturbance source is supported by the four electromagnetic vibration isolators, which suppress the quasi-periodical vibration jointly according to a modified adaptive control algorithm. The experimental results show that the radiated underwater sound pressure can be reduced substantially.