Abstract: A large-deformation compliant mechanism can be used as a nonlinear stiffness element for quasi-zero-stiffness (QZS) vibration isolation. To address the load adaptability issue of QZS isolation, a new approach for constructing dual QZS interval by exploiting nonlinear elastic boundaries based on boundary sensitivity is proposed, and a double-layer compliant isolator is designed. The lower mechanism provides a controllable nonlinear elastic boundary and an axial force release path for the upper mechanism, enabling the upper mechanism to exhibit QZS characteristics in two distinct large-deformation states. An improved chained beam constraint model is employed to establish the nonlinear restoring force model of the double-layer isolator, and the influence of design parameters on the dual QZS characteristics is revealed. The nonlinear amplitude-frequency responses of the isolator within the two QZS ranges are solved using the harmonic balance method. The results show that the isolator can offer low-frequency vibration isolation with an onset frequency as low as 2.3 Hz for payloads in two mass ranges, and it exhibits asymmetric vibration response phenomena under harmonic excitation.