<p>Mechanical properties of granular soil are affected by its relative density and stress level. High confining pressure may lead to grain breakage and further particle rearrangement, which is responsible for the nonlinear deformation behavior. Therefore, an effective hardening law, especially at high stress level, is crucial for evaluating the engineering properties of granular soils and the workability of corresponding geo-structures. In this study, the equivalent concept is firstly introduced into the elasto-plastic modeling of granular materials. An equivalent shifting stress is proposed to estimate the effect of current state on the nonlinear deformation behavior of granular soil. An equivalent hardening law is established based on a classical reference model and implemented into elasto-plastic framework. The proposed model is further extended to a general stress state by using transformed stress method. The equivalent hardening law possesses clear physical meaning, and only one compression test is required for the determination of hardening parameters. Validation has been done by comparing model simulations with the results of triaxial tests under different stress path (e.g., compression, extension, and plane strain tests). It indicates that the proposed model is simple yet effective in reproducing the main features of stress–strain relationship of granular soils, especially at high stress level correlated with significant particle breakage. The introduced equivalent concept can be readily incorporated into other advanced models according to the modeling procedure adopted in this work.</p>