Taking the unsaturated loess obtained from YanLiang district Shaanxi province as the research samples. CT images on structural damage evolution of unsaturated loess were obtained according to the results of the CT scanning and the triaxial shear test of the unsaturated loess. The obtained CT images were divided into five groups based on gray levels and treated through supervised classification method. The evolution of void in three layer sections can be clearly observed from the data of supervised classification. It can be seen that due to the existing of many structural defects such as void, microcracks and ginger like rocks in cross-section of the loess sample, the initial damage is large before shearing. With loess sample shear going on, large void is gradually closed and loess sample is compacted without failure surface, only making some adjustments in the internal structure of soil. The possible reason is that the sample has large moisture content, and soil skeleton is easy to creep and hard to form cracks. The general tendency of structure evolution on loess sample under shear process is as follows: the voids closed, the particle condensates dispersed and the particles realigned, the soil consolidated or worked hardening. This work provides a new experimental method for exploring the structural features of the loess under the triaxial shear conditions from the micro-scale.