The ship springing is continuous vibration of the hull girder due to encountered wave excitation, which is considered as a typical fluid-structure interaction (FSI) problem. In this study, a CFD approach is proposed for modeling ship springing induced by large amplitude regular waves. In the CFD model, nonlinear free surface flows are solved by a finite difference method based on CIP (Constraint Interpolation Profile) method. Flexible structure is calculated using one dimensional finite element method by idealizing the ship structure as a beam. A volume weighted method, which is based on IB (Immersed Boundary) method, is applied to couple the FDM and the FEM. The proposed numerical model is validated against an experiment on a flexible barge in regular waves. Discussions are made on the numerical results.