Abstract: The variation of interior structure of unsaturated natural Q2 loess in triaxial tests was monitored instantaneously,quantitatively and nondestructively by means of computerized tomography(CT) technology.The clear CT images and relevant data reflecting the structure evolution of yield hardening soil samples were attained.The course of yield hardening was explained.It was shown that some structure damages such as pore,flow,ginger nut,etc.existed in natural Q2 loess.The initial structure of Q2 loess was inhomogeneous.The CT data was prominently affected by ginger nut.The meso-deformation of unsaturated natural Q2 loess could be divided into three stages,i.e.,slightly dense stage,stage of slight adjust-ment of structure,and rapidly dense stage.The meso-deformation during the test process was manifested by uniform deformation.A new method to identify the field stress of natural Q2 loess using curves of CT-number versus deviatoric stress or deviatoric strain was suggested.It was suitable to adopt CT-number to describe structure evolution of yield hardening of natural Q2 loess.The variation of CT-number increased with the increase of net consolidation pressure under the same suction;while the variation of CT-number decreased with the increase of suction under the same net consolidation pressure.