Inspired by the biological principle that ostriches can maintain body stability while walking or running on rough terrain, with their limbs playing a role in both load-bearing and vibration reduction, this paper presents a design for a tunable load-bearing bionic limb quasi-zero stiffness isolator, in conjunction with a voice coil motor. Firstly, a static analysis of the structure is conducted to reveal the influence of various parameters on the load-bearing capacity and the range of quasi-zero stiffness. Secondly, considering the kinetic energy and rotational damping of the sliding pair, the system's dynamic equation is established based on Lagrange’s principle. The harmonic balance method is employed to solve and analyze the system's displacement transmission ratio and offset under different parameter conditions. Finally, the accuracy of the dynamic equation and the harmonic balance method is verified through simulations using the Runge-Kutta method and ADAMS, with corresponding vibration isolation performance simulations conducted. The results show that when the load changes, the system's low-frequency vibration isolation performance is effectively enhanced by adjusting the main force of the voice coil motor, keeping the system operating within the quasi-zero stiffness range. Further analysis reveals that the system's offset is highly sensitive to the mass of the sliding pair, and considering the mass of the sliding pair causes the offset curve to have a zero-offset point. These findings provide valuable guidance for the optimal design of bionic limb quasi-zero stiffness isolators in ultra-low-frequency vibration reduction applications and under load mismatch conditions.