Abstract: The effect of vibration loosening on the parametric vibrations of inclined cables is discussed. By the equations of motion considered the flexural rigidity and sag, vibration loosening is numerically calculated by the finite difference method, and the effect of vibration loosening on the principal unstable region and second unstable region of parametric vibration is analyzed. The results show that vibration loosening is generated first at the lower end when the parametric vibration of inclined cable occurs. The minimum support excitation that generates a compressive force varies with inclination angles. Under the support excitation with small amplitudes, vibration loosening easily occurs in the second unstable region of cables with a small inclination angle.