To study the response of submerged floating tunnel tether subjected to random ambient excitation, a non-linear random vibration equation of tether is established considering tether sag. Subsequently, the vibration response of tether is analyzed by means of stochastic equivalent linearization method. The results indicate that, the mid-span displacement and velocity root mean square response of tether subjected to zero-mean Gaussian white noise excitation tends to stable value after a certain period of time, while the cross-correlation function of mid-span displacement and velocity tends to zero; the mid-span displacement root mean square response of tether decreases as its damping ratio increases，whereas it increases as power spectral density of excitation increases; due to the existence of water damping force, the displacement and velocity root mean square response of tether decreases rapidly compared with tether in air.