A nonlinear three parameter isolator geometrical nonlinear characteristics is provided by using X-shaped structure for further controlling dynamic responses near the resonance frequency when the isolation performance in high frequency band is kept unaffected.A compound dynamic model of nonlinear three parameter isolator with the X-shaped structure is presented.The analyticalexpressions of the nonlinear three parameter isolator's dynamic responses are derived by using the harmonic balanced method(HBM).The effectiveness of the analytical solutions of the nonlinear three parameter isolator model is verified by comparing withthe simulation solutions and experimental data in time domain.Compared with the traditional two parameter and three parametercounterparts,the nonlinear three parameter isolator can reduce the resonance amplitude apparently and shift the corresponding peakfrequency to higher,meanwhile,exhibit limited effect on isolating performance in high frequency region.In the next section,thisresearch puts focus on the ffects from the designing parameters that is stifess ratio y?and y?,damping coefficient C,initial angle0:and the excitation force amplitude Foon the force transm issibility of the nonlinear three parameter isolator model.The calculatingresults show that stiffness ratio y?and y?,damping coefficient Caand initial angle0,the stifress ratio can be used to adjust the isolating performance of the nonlinear isolator effectively.However,the influences of the excitation force amplitude Focan be ignored.The vibration isolation performance of the nonlinear three parameter isolator outperforms than the traditional one when choosingproper design parameters around the resonance frequency,while the dynamic performance will not be changed in the high frequency region.