<p>This study presents a systematic investigation into the mechanical response of geogrid reinforcement within a two-stage reinforced soil abutment system under static loading conditions. Leveraging field monitoring data from a practical project, a FLAC3D finite difference model was established and its reliability was verified (the error between the measured displacement and the simulated value being less than 8.2%). The interaction mechanism between the reinforcement material and the fill soil was revealed. The study integrates the limit equilibrium theory and numerical simulation methods and develops a calculation framework that can predict the potential failure surfaces of the geogrid-soil composite material under different geometric configurations. Based on the stress diffusion theory, the analytical formula for the lateral earth pressure distribution that considers the influence of step width (0.0–9.0&#xa0;m) was derived. Further, by combining Hooke’s law and the principle of virtual work, a quantitative prediction model for the internal and overall horizontal displacements in the reinforcement zone was established, and the calculated values show a similar trend to the simulation results. The results indicate that the steps have a significant impact on the mechanical properties of the composite material system, and the optimal performance occurs under specific geometric ratios. This research provides fundamental insights into the material performance characteristics of geogrid-soil composite materials and establishes a theoretical framework for the design and analysis of foundation-enhanced infrastructure systems.</p>