Abstract: A cylindrical composite foundation structure was presented and the effect of base impedance on the foundation damping performance were predicted through impedance theory analysis.The stiffness characteristics of the foundation,plate frame and hull girder were outlined through experiments or FEM.Adopting vibration level difference as evaluation index,the effect pattern of the base impedance on the damping mechanisms of the foundation prototype installed on two bases were investigated through vibration tests.The results show that comparing to the plate frame base,the damping performance of the foundation installed on the hull girder base increased 6dB,and axial damping capacity of the core material is more favorable,especially at high-frequency.