Abstract: To study the transversal oscillation response of the tether under vortex-induced vibration and parametric vibration, a nonlinear tether-tube model of submerged floating-tunnels is proposed by the basis of taking the sag of the tether into account. Numerical analysis and solutions are presented by Galerkin method and Runge-Kuta integration method. It may be concluded that the vortex-induced vibration of the tether may excite the parametric vibration of the system; the initial disturbance of the system has a significant effect on the transient amplitude of the tether; the steady-state vibration amplitude of the tether is determined by the vortex-induced vibration; the response under the combined action of vortex-induced vibrations and parametric vibrations is larger than that of any single vibration.