Inspired by the safe landing of a cat falling from a high altitude,a bio-inspired polygonal skeleton(BIPS)structure is proposed,and its nonlinear characteristics are systematically studied to explore its potential application in the suppression of vibration.The polygon is formed by the skeleton structure of the cat's entire body and the ground.The BIPS system consists of two symmetrical bionic legs with three robs(as skeleton)and four horizontal springs(as muscle).Two bionic legs are connected through the bearing platform(as spine),which could adjust the distance between the two bionic legs.A theoretical model is developed to characterize its stiffness nonlinearity through geometrical and mechanical analysis.Parameter analysis reveals that the BIPS structure has diverse stiffness,including nonlinear positive stiffness and negative stiffness.By imitating adjustment of leg posture and telescopic function of the spine(control the distance between legs),these flexible stiffness properties can be adjusted by structure parameters.In addition,the load capacity and working range can also be designed by the length of the bars,the initial angle,the mounting position,and the spring stiffness.The experimental setup is established,and the vibration isolation performance under various excitation is tested.The experimental results verify the accuracy of the dynamic model and also show that the proposed BIPS structure can suppress the vibration effectively under a variety of excitations.These peculiarities may provide potential possibility of an innovative approach to passive vibration control and isolation.