To address chronic neck injuries in pilots caused by repeated high-G impact, a design methodology for cable-based protective gear based on a head-neck-protective device coupling model was proposed. Worn between the pilot's head and shoulders, the protective device's efficacy was influenced by human-machine dynamic interactions, necessitating consideration of coupling effects during design. Based on Lagrangian dynamics, a coupled dynamic model simulating the coordinated response of the head-neck region and the device under external impacts was established. This model analyzed the influence of key device dimensions on the dynamic response of the neck. Subsequently, to achieve an optimized design, the neck injury criterion (NIC) was employed to evaluate the protective effectiveness of the device at different mounting positions on the head and shoulders. Finally, a human head-neck experimental platform was constructed to validate the optimized design results. Results demonstrate that the coupled model is applicable for device design, and the optimized outcomes effectively reduce neck injury risk. This design approach establishes a protective device design framework encompassing human-machine dynamic interaction processes, offering new insights for similar protective device designs.