Abstract: On the basis of disturbed state concept for saturated soils,a new expression form of coupled disturbing variable for unsaturated soils is defined in this paper,in which both of disturbance factors that external force and wetting are considered. Moreover,a new constitutive model of unsaturated intact soils is build up in accordance with homogenization theory for composites materials,and the evolution equation of the coupled disturbing variable is proposed. Comparing the calculation results of BBM and this model with the experimental results respectively,it can be seen clearly that this model can better simulate the mechanical properties of unsaturated intact loess. In addition,according to the analysis results of the influence of structural parameters on shear behavior,the degradation law of soil structure can be well described by the proposed evolution equation of coupled disturbing variable.