Abstract: The formulas of the squeeze film damping and viscous damping are derived by solving the motion equation of a heat exchanger tube enclosed in a concentric sleeve with (N -1)concentric support plates. An experimental study of squeeze film damping and viscous damping for a four span heat exchanger tube enclosed in a concentric sleeve is carried out in quiescent water in order to verify the result of theoretical analysis. The relationship of viscous damping with the inner diameter of concentric sleeve and tube - sleeve eccentricity is presented. The relationships of squeeze film damping - support plate thickness and tube - support plate hole eccentricity as well as tube - support plate hole clearance are obtained on the basis of experimental result. The design sizes of heat exchanger tube spacing, support plate thickness and support plate hole clearance are presented for reference.