[Objective] To study the influence of water medium on the vibration characteristics of a double cylindrical shell with vibration isolator. [Method] Based on the finite length double cylindrical shell model, the FEM/AML technology and the "double shell method" are used to calculate the mean square velocity of the shell. [Result] The results show that the outboard water medium reduces the vibration amplitude of the shell; the vibration short circuit of the interboard water medium reduces the vibration isolation performance of the vibration isolator; the combination of air bag and vibration isolator based on equivalent air layer can effectively improve the performance of low frequency vibration isolation. [Conclusion] The results have a certain guiding effect on the design of vibration isolation system of double cylindrical shell.