A high damping vibration isolator with nested X-type structure is proposed for the first time in order to achieve the high damping output vibration isolation of isolators without reducing stiffness. On the basis of the established dynamic model of vibration isolation system, firstly, the equivalent damping of vibration isolation system is derived, and its nonlinear variation characteristics are studied. Then, the harmonic balance method is used to obtain the force transmissibility of the vibration isolation system. Based on the force transmissibility, the performance of vibration isolation and the sensitivity of design parameters are analyzed. Finally, the validity of the theoretical model and the accuracy of the analytical results are verified by the performing experiments. The results show that, compared with the conventional linear isolators，the nested X-type structure high-damping isolator with the same design parameters can greatly improve the damping output, and its isolation characteristics can be flexibly adjusted by various design parameters. The research results can provide theoretical basis for the design and application of high damping vibration isolators.