In present，a series of uniaxial compressive experiments on sandstone samples have been conducted in the laboratory by using jointed devices of triaxial loading equipment and medical SOMTOM-plus CT scanner. Based on CT value, expression of density damage variables and density damage increments (DDI) of brittle rock and the method to determine the rock initial damage variables have been worked out. From real-time CT observations of sandstone sample under uniaxial compression condition and the analysis on CT digital images and the relation curve between sandstone density damage increment (DDI)and stress, the evolution process of fracturing in brittle rock sample can be divided into five stages, i.e. initial densification stage, crack occurrence-propagation, crack merging-bifurcation, crack rebifurcation-propagation, and crack cut-through-massive failure stage. Crack occurrence-propagation is a local phenomenon and the whole rock is still in the densification stage. Therefore, the rock failure process under compression is mainly including three stages, namely initial damage densification, local dilatation-bulk dilatation, and massive failure. The use of CT images and relation curve between density damage increment and stress in analyzing the meso-damage evolution processes of brittle rock sample is an important and effective method. As an important mechanics index in rock meso-mechanics, the density damage increment can be used to analyze the quantitative fracturing process in brittle rock under compressive condition, as well as being an important factor in a rock fracturing process model to be constructed.