Abstract: A submerged body, which interacts with the surrounding water, is essentially one of the Fluid-Structure Interaction (FSI) problems. The displacement-pressure pattern, in which the structure and the fluid are described by the displacement and the pressure respectively, is used to model the submerged body. A large un-symmetric equation is introduced as a result of this pattern and the finite element method (FEM). To get the dynamic characteristics of the submerged body, the Arnoldi method is adopted to solve for the eigenvalues of such a large unsymmetric equation. In addition, the shift-frequency technique with a special iteration pattern is contrived to overcome the zero frequency problem resulting from the rigid body抯 motion. Finally, a numerical example, in which there is a long cylinder with two cones at both ends, is given out to validate the methods in this paper.