<p>The shear strength of unsaturated soils is a key factor in evaluating slope stability; however, hydraulic hysteresis induced by varying rainfall infiltration conditions remains a major challenge for accurate strength prediction. To address this issue, a hydraulic history-dependent intergranular stress model is developed. The proposed framework integrates a state-dependent soil–water retention model that effectively characterizes both capillary hysteresis and air entrapment effects, enabling precise tracking of the hydraulic paths with a minimal number of fitting parameters. The model is validated through a series of direct shear tests on compacted loess samples subjected to controlled drying and wetting processes. The results reveal distinct strength discrepancies between paths: Specimens along drying paths consistently exhibit higher peak shear strength than those along wetting paths at equivalent water contents, with a maximum difference of approximately 21 kPa. This strength variation arises from hysteresis-induced differences in matric suction and is closely associated with the magnitude of the soil–water retention hysteresis loop, reflecting hydraulic history and physicochemical interactions among soil phases. Comparative analysis under both effective stress and dual stress frameworks demonstrate that the proposed model achieves superior predictive accuracy, with <i>R</i>² values exceeding 0.97 across all hydraulic paths. By accounting for both instantaneous hydraulic states and historical moisture variations, the model provides a robust and reliable framework for evaluating the shear strength behavior of unsaturated soils under complex hydraulic conditions.</p>