Abstract：Natural sedimentary loess has structural properties，and it shows different mechanical properties before and after structural failure. Laboratory tests are performed to reveal the structural properties and collapsible deformation characteristics. The yield function and damage function of the unsaturated loess are established based on the principle of loess damage evaluation principle，the relationship between stable porous ratio and stable state of wholly-disturbed saturated clay，and the fact that inverse deformation is caused by the slip and crash among masses. The constitutive mathematical model of unsaturated natural loess is set up，by which loading process and other properties can be simulated. This model has clear physical meaning and the numerical calculation by it agrees well with tests.
