To reduce the radiated waterborne noise and improve the capability of acoustic stealth of ships, the method can be implemented conveniently and effectively by inserting isolators between the vibration source and the base. A dynamic model for twodegreeoffreedom vibration isolation system with nonlinear spring was established. The vibration transmissibility and the isolation effectiveness of the system are analyzed. Bifurcation diagrams of the system with different excitation amplitude f1 were gained and the dynamic behaviors with different excitation frequencies ω were also obtained by numerical method. The research results reveal that chaotic motion of the system appears at the 1.12～1.18 frequency component when f1=12.0, and the reduction of the line spectrum in chaotic state is much greater than that in nonchaotic state and the isolation effectiveness of the system is eminent. The application of chaos method in line spectrum reduction is preferably validated.