<p>The coconut structure exhibits inherent impact resistance, with the macroscopically ordered distribution of variable cross-section fibers in its husk playing a crucial role in stress wave propagation and scaling. Inspired by the natural structure and fibers, this study proposes a stress wave propagation model for a variable cross-section bar considering viscous effects. A theoretical model for stress wave propagation in a fusiform-shaped bar with variable cross-section is established, elucidating the stress wave scaling effect observed in coconut fibers. Additionally, a quasi-one-dimensional method for analyzing and measuring stress wave propagation is introduced, and an experimental setup is assembled. Experimental validation of the stress wave scaling effect confirms the theory’s accuracy for stress wave scaling in variable cross-section bars. This research provides theoretical guidance and measurement methods for the design of space landers, automobile anti-collision beams, stress wave collectors, and scalers, as well as for impact testing of macro and micro materials and the design of sustainable plant-based materials for impact protection.</p>