Disc spring vibration isolators are often simplified as linear models in practical engineering. With the increase of the number of disc springs in the isolator，the boundary friction effect and nonlinear stiffness and damping problems lead to the distortion of the linear model. In order to study the nonlinear vibration characteristics of opposed disc springs with boundary friction，a vibration isolator with opposed disc springs of pre-tightening is proposed. A nonlinear dynamic model of this vibration isolator under considering boundary friction and pre-tightening is established. Klotter’s method is applied to solve the nonlinear equations，and the forced vibration of the vibration isolator with opposed disc springs under based excitation is analyzed and calculated. Based on Routh-Hurwitz stability criteria，the instability interval of the vibration isolator with opposed disc springs is deduced and calculated. The influence of the system parameters on the nonlinear vibration and stability interval of the vibration isolator is also discussed. The results show that the amplitude-frequency characteristic curve and the stability interval are only influenced by the nonlinear stiffness cubic coefficient α2，viscous damping coefficient μ1 and additional support force coefficient μ2 of the system. And the square of break-loose frequency Ωb of the system is proportional to the additional support force coefficient μ2. The system with opposed disc springs exists abnormal jump and non-resonance state which does not jump to stable resonance branch. And the relationship between viscous damping coefficient，additional supporting force coefficient on those two states and their stable intervals are explained. The accuracy of the model is verified through fixed frequency tests.