<p>Particle crushing, occurring in crushable materials under high-stress conditions exceeding their crushing strength, leads to particle breakdown and reduction in peak shear strength. The presence of water further diminishes crushing strength. Additionally, particle crushing significantly alters the soil–water characteristic curve (SWCC). The combined effects of particle crushing and the degree of saturation changes induce excessive deformation and weaken the soil. While existing models can predict the behavior of unsaturated soil and particle crushing effects individually, a comprehensive model for unsaturated crushable soils is necessary. This study proposes a constitutive model for unsaturated crushable soils, integrating the effect of the degree of saturation on crushing strength by developing the crushing surface. It incorporates variations in the grading state index and the degree of saturation, affecting soil strength via state boundary surface movement. Validation is achieved through past experimental evidence. The model effectively captures key features of unsaturated crushable soils, including the reduction in crushing strength with increased degree of saturation, the evolution of SWCC due to particle crushing, and additional particle crushing during wetting. Furthermore, a parametric study offers insights into unsaturated crushable soil behavior, highlighting the combined effects of particle crushing and variations in the degree of saturation. When significant particle crushing occurs, increased volumetric compression due to particle crushing leads to a higher degree of saturation and further strength reduction, amplifying soil deformation. Understanding these interactions is crucial for predicting the behavior of unsaturated crushable soils, emphasizing the significance of this study.</p>