Abstract: Free vibration and forced vibration characteristics of finite cylindrical shells semi-filled with liquid are studied in this paper, based on the energy functional variational principle.The combined form of the triangular series and the Fourier series is used to represent the displacement of the cylindrical shell, and the orthogonality is then used to eliminate the displacement on the other two directions after the variation, where only the radial displacement is kept.The relationship between the amplitudes of fluid load and the amplitudes of the radial displacement is established with the orthogonal processing of the continuous conditions of the solid-liquid coupling contact surface and the boundary conditions of the free liquid surface.Finally, the fluid structure coupling control equation is obtained.The results show that the proposed method is both correct and effective;in addition, it provides a new thought for solving similar problems.