Slate is a common geological material in geotechnical engineering. Traversed by joints and schistosities with clay minerals,the mechanical characteristics of slate are complex;and the existence of the numerous microscopic cracks and voids aggravates the complexity. Using the loading equipment corresponding CT machine,the CT real-time tests of two unsaturated jointed slate samples from Jinping-II Hydropower Station under triaxial compression are conducted. The typical CT images in failure process are obtained. With the obtained CT images,the evolution processes of crack initiation,propagation,coalescence,and finally macroscopic fracture formation are analyzed in the microscopic scale;and the differences of failure mechanisms with different strata distributions are explained. Based on the principle of CT,the scalar damage variants of unsaturated rocks are presented with the CT values.