Purpose <p>To broaden the isolation band of low frequency vibrations with line spectrum characteristics, this paper proposes a nonlinear enhanced bellows-type hydraulic <i>Inerter-based Dynamic Anti-resonance Vibration Isolator</i> (I-DAVI).</p> Methods <p>First, the nonlinear dynamics model for the novel device is established and the mathematical expression for the nonlinear elastic restoring force of the bi-stable springs is derived by using quasi-static analysis. Then, influences of geometric dimensions and elastic coefficient of bi-stable springs on the nonlinearity characteristics are studied. Next, the vibration transmissibility of the degraded linear I-DAVI system under force excitation is analyzed. Furthermore, the dynamic response for the nonlinear enhanced system is obtained analytically via the averaging method, and analytical solution steps for the nonlinear transmissibility are provided based on the equivalent linearized stiffness method. Finally, the comparative study is carried out for systems with different parameters.</p> Results <p>The relevant result reveals that the inclusion of additional springs with negative stiffness only affects the extent of nonlinearity in the stiffness curve, and the transmissibility are dominated by three dimensionless parameters including inertial mass ratio, effective area ratio and damping ratio. The comparison with numerical results shows that analytical results exhibit relatively small relative errors and can be used for design purpose.</p> Conclusion <p>Compared to the purely linear I-DAVI system, the proposed enhanced nonlinear isolator can broaden the frequency isolation band through shifting resonance and anti-resonance frequencies towards zero frequency without reducing the loading capacity or increasing static deformation. By designing appropriate inertial mass parameters, efficient wideband isolation effectiveness can be achieved in the low-frequency band.</p>