Abstract: In order to obtain the exact solution for the vibration and sound radiation of composite sandwich cylindrical shell, the shell was divided into several thin layers in the thickness direction, the state space equation was established for each thin layer based on three-dimensional elastic theory and state space technique and the transfer matrix of transversal displacement and stress was built considering the continuous condition of displacement and stress. The fluid load on the outer surface and the point excitation on the inner surface were expanded by Fourier series and introduced into the state space equation, the exact elastic solution of underwater vibration and sound radiation of composite sandwich shell was obtained. In contrast to the results by finite element simulation and that from the previous literature, present theoretical model is more accurate than the approximate two-dimensional shell theories. The effect of ply angle, thickness distribution of face and core and loss factor on vibration and sound radiation were further investigated. The results show that in the frequency range below the ring frequency the peak's number of sound power changes as the parabolic curve, and in the middle and high frequency bands above the ring frequency the peak's number of sound power increases first and tends to be gentle, and then continues to increase. With the increasing of core's loss factor, the peak value of sound radiation power gradually decreases, as well as the extent of decline.