Abstract: In order to investigate the fluid structure interaction problems occurring in tube bundles, a numerical model is presented. The unsteady three-dimensional Navier-Stokes equation and LES turbulence model are computed with finite volume approach on structured grids combined with the technique of dynamic mesh. The model presents a three dimensional fully coupled approach with solving the fluid flow and the structure vibration simultaneously, for the tube bundles in cross flows. The results show that, the presented model is validated with experimental data and compared with existing models in the literature. Trajectory of single tube is "8" shape at "locked in". The two parallel tubes oscillate in opposite phase and both have the same amplitude. For pitch higher than 1.5D, there is no mutual influence of the tubes and response is close to the case of single tube. The lift force and amplitude of downstream tube of two inline tubes are increasing as the pitch increases. The upstream tube is almost not influenced by the downstream one when the pitch is larger than 2D. The fluid force and response are close to the case of single tube.