Abstract: While studying the underwater acoustic radiation from cylindrical shells，the fluid is often assumed to be infinite. However，the free surface of the fluid always exists in real practices. Aiming at this flaw in the assumption，the structure-acoustical coupling equation of a cylindrical shell submerged in the fluid with finite depth is established by applying the image method and the addition theorem of the Hankel function，based on the Flügge equation and the Helmholtz equation. The fluctuation characteristics of the sound pressure at a certain observation point versus the depth are investigated，and it is found that the distance between the two adjacent peaks in the obtained curve equals half of the acoustic wavelength in the fluid. These findings may provide a theoretical basis for practical engineering applications.