Abstract: Soil structure can improve the stability of soil skeleton. Hence, the void ratio of structured soils is usually higher than that of the reconstituted soils under the same effective stress. Based on the process of the formation of structured soils, the influences of the soil structure on the deformation characteristics are analyzed. Besides, the destruction law of the soil structure in the process of deformation is investigated. A quantitative parameter of the soil structure (relative structure degree) is proposed. The evolution equation for the new parameter during the deformation is obtained according to the experimental data. The volume change equation for the structured soil is derived by incorporating the new parameter. The volume change equation describes the change of the soil structure and compression index of structured soils during deformation. The constitutive model under triaxial stress state for the structured soils is derived by incorporating the modified cam-clay model. The mechanical and deformation behaviors of the structured soils are captured by the proposed model. The new constitutive model is able to predict the mechanical behaviors of the structured soils through the comparisons between the numerical results and the experimental data from three kinds of natural structured soils.