A new method to calculate the volumetric strain of collapsible loess considering microstructure instability is developed. In this method

loess is regarded as the compound of disturbed part and undisturbed part. The volumetric proportion of the both parts

which represents the state of micro-structural damage and varies with the increase of effective load

can be calculated by the combination of an idealized microstructure model

the pore size distribution curve and the equilibrium criterion for microstructure. The method is verified by comparing the calculated results with the data of triaxial compression tests. In addition

some experiments show that compression curves of loess with different water contents are parallel with each other in the sections that represented progressive damage to microstructure. This phenomenon is successfully explained by the equilibrium criterion for microstructure.