In order to enhance the precision of the dynamic model of a raft vibration system, this paper introduces the concept of free velocity. We utilized the method of four-end parameters in order to establish the model of raft frame and base. Then, we formulated the dynamic equations of the global flexible floating raft system based on impedance synthesis analysis. We calculated a numerical sample to demonstrate the efficiency and accuracy of the proposed method. Finally, we discussed the influence of the flexibility of the raft frame and the stiffness of the isolators on isolation efficiency.