An X-shaped structure is applied to quasi-zero stiffness isolator to improve its low frequency isolation performance. The dynamic equation of the system is established by using the Newton’s motion law. The amplitude-frequency response curves of the system are obtained by using the incremental harmonic balance method. The effect of equivalent reduced stiffness γ on system transmissibility is discussed. Research results show that the reasonable numerical interval of dimensionless pre-compression length of horizontal spring is (0， 2). In the resonant region， the increase of γ can significantly reduce the force transmissibility. At higher excitation frequencies， the effect of the change of γ on the vibration isolation performance of the system is weak. With the decrease of γ， the displacement transmissibility in the resonance region decreases sharply. In addition， the decrease of γ will also reduce the resonance frequency and make the jump phenomenon disappear. Therefore， the equivalent reduced stiffness γ of the X-shaped quasi-zero stiffness isolator is an ideal parameter which can effectively reflect the effect of low-frequency vibration isolation of the system. The effect of equivalent reduced stiffness γ is discussed in detail.
