Soil structure is one of the physical properties of the soil, which represents the spatial arrangement of soil particles and the type of inter-granular cementation, and it plays an important role in influencing the mechanical properties of collapsible loess. As it is closely linked with density, particle and moisture, the soil structural can reflect the change of the mechanical properties such as strength and deformation. The structural variations induced by either the passively wetting or the positively loading are investigated, with adopting the stress ratio structural index that accounts for the overall structural potential of the soil. Firstly, the structural evolution of loess is determined under compression, shearing and wetting conditions; then the effect of structure on the soil behavior is characterized by establishing a correlation among the stress-strain behavior, yielding and failure behaviors and the soil structures; finally, the structural constitutive relationship of loess under wetting and loading conditions is developed. The proposed model is validated by comparing the numerical results with the experimental data and the results of the modified Cam Clay model.