Abstract: A new facility in a laboratory is described that measures the acoustic properties of underwater acoustical materials in the frequency range from 10-100 kHz, at hydrostatic pressure to 3.0 MPa. And the typical size of material sample is 300×300 mm². By using plane transducer arrays composed of many elements, two large acoustically transparent PVDF films hydrophones and broadband narrow pulses together with the technique of modern signals processing, an approximate plane-wave free field is built in a small pressure vessel. So, the variance of acoustic properties of material as a continuous function of frequency at a hydrostatic pressure can be obtained. The acoustic parameters include complex reflection and transmission coefficient (echo reduction and insertion loss), attenuation coefficient, complex acoustic impedance and sound speed. Measurements are made on a number of samples with widely varying properties to illustrate the capability of this facility. Its stability is also checked and the results show that the expanded uncertainty in reflection and transmission measurement is 1.2 dB and 0.8 dB.