Duncan- Chang model based on classical continuum theories cannot reflect the softening behavior ofgeotechnical materials and it lacks the parameters describing the failure of materials and the internal length scale re-lated to strain localization.In order to solve this problem,on the basis of the disturbed state concept and by intro-ducing the Cosserat continuum theory as a regularization mechanism,the response of materials in relative intactstate is described with the Duncan- Chang model,the mechanical behavior of materials in fully adjusted state ischaracterized with the critical state model,and two disturbance evolution modes,one of which is based on the volu-metric strain threshold as well as the conventional triaxial test curves and the other is based on the limit state of de-viator strain energy,are presented.Moreover,some numerical examples are given to reveal the effects of distur-bance on the bearing capacity and the strain localization behavior.The results show that both of the two disturbanceevolution modes well describe the softening behavior of materials,the latter mode is more reasonable than the formerin terms of the inclination angle prediction of shear band,and the developed disturbed state model above helps toreduce the mesh density- dependence of the results to a certain degree when it is used to simulate the strain localiza-tion phenomenon.