Abstract: Inspired by the “M-shaped” structure of bird legs, a semi-active bio-inspired quasi-zero stiffness ultralow-frequency vibration isolation system integrated with an electromagnetic damper is proposed. It effectively addresses the challenge that traditional ambulance stretchers face in balancing vibration reduction performance and static load stability during low-frequency isolation. First, the mechanical characteristics of bird legs are modeled as a quasi-zero stiffness system. By introducing the dynamic damping regulation mechanism of an electromagnetic damper, a semi-active vibration isolation system is constructed, featuring high static stiffness for load-bearing, low dynamic stiffness for vibration reduction, and adjustable damping. The harmonic balance method is employed to analyze how key parameters, such as the damping ratio, influence the stretcher system's vibration isolation performance. On this basis, nonlinear backstepping algorithm and damping force tracking control strategy are adopted to achieve nonlinear semi-active vibration reduction control, effectively expanding the vibration isolation frequency band and enhancing system stability. Finally, bench tests on dynamic characteristics and vibration reduction performance are conducted. The results demonstrate that the proposed semi-active bio-inspired quasi-zero stiffness ultralow-frequency vibration isolation system and its control strategy significantly improve the stretcher's vibration isolation efficiency and stability, while effectively preventing the unstable jump phenomenon in nonlinear systems.