Abstract: Noise reduction by means of applying flexible coating on underwater structures is commonly used in the marine field. In order to provide theoretical references for the selection of evaluation indicators of noise reduction performance of flexible coating, a vibration and acoustics model of a simply supported underwater rectangular plate covered by flexible coating, excited by a point force, is established, and the five potential evaluation indicators are defined. Only one indicator, vibration transmission loss, is independent on the length, width of the plate and the location of point excitation force, and vibration transmission loss can describe well the performance of flexible coating to isolate the fluid from the vibration of the base plate. Another indicator, wet surface quadratic velocity insertion loss, compares better with sound radiation power insertion loss than vibration transmission loss, especially at low frequency. Thus, as evaluation indicators, vibration transmission loss and wet surface quadratic velocity insertion loss have respectively their own advantages and disadvantages.