Water-filled impedance tube is an important testing facility for underwater sound absorption materials.However,most water-filled impedance tubes can only meet the requirements under normal hydrostatic pressure,and it still faces some challenges for testing under high hydrostatic pressure.Especially,the high-pressure sealing problem is the key.The high-pressure seal device of the water-filled impedance tube was designed,in which the sleeve seal was adopted for the mounting tube seal of hydrophones,the O-rings were adopted for the seal of the top flange with the sample holder and the bottom flange with the underwater transducer.This design can not only improve the sealing performance of the water-filled impedance tube,but also guarantee the fast and convenient installation of the hydrophone and the sample.The hydrostatic pressure test shows that the designed water-filled impedance tube can meet the sealing requirements under 3.15 MPa without obviously pressure dropping or water leaking.The underwater acoustic test indicates that the water-filled impedance tube has good stability in the test of underwater acoustic materials at high hydrostatic pressure up to 1.5 MPa.This research provides a reliable test basis for the design and improvement of the seal of water-filled impedance tube．