Abstract: In order to investigate the flow induced vibration problems in tube bundles, a numerical model for fluid-structure interaction system of an in-line square tube bundle was presented. The unsteady three-dimensional Navier-Stokes equation and LES turbulence model were solved with finite volume approach on structured grids combined with the technique of dynamic mesh. The dynamic equilibrium equation was discretized according to the finite element theory, and the properties of fluid force and responses for various elastic tube models were studied by several calculations. The results show that tube configurations have an important effect on fluid force and dynamics respond. The 5-tube model can basically represent a flexible tube bundle. The critical velocity predicted by single tube model is larger than that predicted by flexible tube bundle. Besides, it shows good qualitative agreement on flow induced vibration behaviors of square bundle with a pitch-to-diameter ratio of 1.5.