Abstract: Numerical prediction of the natural vibration characteristics of ring-stiffened and axial stiffened cylindrical shells and conical shell with different boundary conditions and being immersed in air and water and filled with water were conducted. Within this process, numerical precision of calculations were validated. Results show that numerical precision of dry modal analysis over the frequency range of 2 kHz and wet modal calculations with one or two-side added water in the range of 500 Hz is limited with a maximum difference less than 10%. Natural vibration of cylindrical shell coupled with fluid-solid interaction (FSI) can be processed by solid or shell mesh element, wherein the solid element discretization method qualifying a little higher precision and a winder efficient frequency range compared with that of shell element method with the cost of a lot more work. The natural vibration analysis of shell structure with diameter- to-length ratio bigger than 0.2 immersed in water is able to be switched into the case of filled with water with equal wetted surface area to decrease the computational load including partial FSI interface. The ring ribs and static fluid load significantly affect the natural vibration of cylindrical shell including both the natural frequency and modal shape, exactly speaking, the ring ribs inducing an increase of natural frequency whilein a contrary direction for the fluid load with a bigger rate. The phenomenon of different order of modal shape exists for both of the two affecting factors. The effect of FSI on natural frequency of cylindrical shell with or without ring ribs is considerable. Compared to the case of being contacted with one side water, the cylindrical shell contacted with two-side water shows a further reduction of natural frequency but the modal shape basically unchangeable. The effect of fluid load on natural frequency and modal shape for conical shell is smaller than that for cylindrical shell.