Abstract: Taking the sag of a tether into consideration, the non-linear vibration equation of a submerged floating tunnel tether caused by axial excitation is derived. The numerical analysis and solutions of a typical tether are presented by the Galerkin method and Runge-Kutta integration method. It may be concluded that the parametric vibration response of a submerged floating tunnel tether is related to the water damping force, tether sag and axial excitation; that the ratio of internal and external diameters of the tether should be chosen by a comprehensive consideration; that the computation results without considering the tether sag are smaller, compared with those of considering sag; and that parametric vibration response of submerged floating tunnel tether due to a water damping force is smaller than that of the tether on land.