Abstract: Objectives In the vibration isolation test of large non-constrained metal bellows expansion joints (hereinafter referred to as metal expansion joints), due to its easy instability when filling pressure, the test tooling that is to balance the huge blind force generated by the internal pressure, and can not be completely fixed at both ends of the metal expansion joints, the test is difficult, and there is a lack of standard test methods, so a test device is designed to test the vibration isolation effect of large non-constrained metal bellows expansion joints. For this reason, a test device is designed to test the vibration isolation effect of large non-constrained metal bellows expansion joint. Methods The double-metal expansion joints are supported against each other, and both ends are fixed by the pedestal support to achieve axial stabilization, and two different limiting methods, namely, bearing cable and airbag, are designed to prevent radial instability. The axial and radial excitation of the metal expansion joints under pressure is carried out by using the shaker, and the acceleration response of the metal expansion joints in the frequency range of 10Hz~315Hz under the two limiting methods is collected, and the difference in vibration level between the input end and the output end is calculated. Results The test results show that the total vibration level drop measured by the bearing cable and the air bag device decreases with the increase of the internal pressure of the metal expansion joint, and the total vibration level drop of the air bag device under the internal pressure of 0P, 0.8P and P increases by 8.59dB, 5.70dB and 4.80dB, respectively, in the axial excitation direction of the bearing cable device. In the radial excitation direction, 4.32dB, 3.57dB and 4.95dB were increased respectively. Conclusions The designed test device can obtain the vibration isolation performance of large non-constrained metal bellows expansion joints, and the airbag limiting device has less influence on the vibration level drop than the bearing cable limiting device, so it is suggested that the large non-constrained metal expansion joints vibration level drop test device adopts the radial limiting of the airbag to obtain better measurement results.