Abstract: Quasi-zero stiffness structures exhibit high static stiffness and low dynamic stiffness. They maintain high static stiffness while exhibiting low dynamic stiffness near the static equilibrium position, thereby resolving the challenge faced by traditional vibration isolation technologies in achieving both adequate stiffness and load-bearing capacity during low-frequency isolation.Current research on quasi-zero stiffness primarily focuses on achieving high static and low dynamic characteristics through large-scale independent spring mechanisms. However, miniaturizing and installing such spring mechanisms remains challenging for micro-instruments or instruments requiring continuous load-bearing.To overcome this issue, this study proposes a novel Cosine Beam Quasi-Zero Stiffness Metastructure (CBQM). Its quasi-zero stiffness property arises from the coupling of two distinct mechanical characteristics: negative stiffness resulting from the double cosine beam's sudden bounce behavior, and nonlinear positive stiffness dominated by the bending of the mirror-arranged double cosine beams.The mechanical properties of this metastructure were theoretically derived by establishing a mechanical model of its monolithic structure. The validity of this theoretical model was verified through numerical simulations and experimental validation. Results indicate that the experimental platform force deviated from theoretical values by only 4.3%. Furthermore, compared to designs with linear positive stiffness, this structure achieved a 25.6% increase in platform force, fully demonstrating the advantages of nonlinear positive stiffness.Building upon this foundation, we further investigate the influence of structural parameters on mechanical properties. By integrating simulation and experimental studies, we explore the regulatory mechanism of quasi-zero stiffness effects through the arrangement of array units. Simulation and testing reveal that horizontal unit arrangement enhances load-bearing capacity, while vertical arrangement broadens the quasi-zero stiffness range. This pattern endows the overall structure with programmability.This study utilizes the nonlinear stiffness coupling of a cosine beam structure to achieve high-stiffness static mechanical properties with a wide quasi-zero stiffness range, providing significant guidance for designing load-customized quasi-zero stiffness metastructures.