The purpose of this study is to propose the numerical simulation method of computational fluid dynamics in order to solve the unsteady state undergoing elastic deformation of interforcial object. This study employs GCL (Geometric Conservation Low) method because metrics and Jacobians should be evaluated in the finite volume method to satisfy the conservation in the discretized form of Navier-Stokes equations. And to solve the elastic deformation the finite element method is used. So this problem is solved the fluid-structure weak interaction analysis using both FDM and FEM.