Abstract: This paper studies the meso-damage and deterioration mechanism of rocks under freezing and thawing. First, the computed tomography (CT) images of red sandstone was obtained based on CT scanning test using. Then, the images were analysed by using image processing technology of three-dimensional reconstruction, and the porosity and fractal dimensions that characterize the meso-structure of the rock were obtained. And then the damage evolution law of red sandstone under the freeze-thaw environment was studied after adopting a fractal dimension to depict the damage variable of freeze-thaw rocks. Results show that: 1) through image processing and three-dimensional reconstruction technology, a three-dimensional reconstruction model that characterizes the macroscopic damage and deterioration of the rock and the development of the mesopore structure can be obtained; 2) the damage evolution corresponds to the development of pores inside the rock mass, in other words, with the increase of freeze-thaw cycles, the porosity of red sandstone increases gradually, and the fractal dimension decreases gradually; 3) the freeze-thaw rock damage variable defined based on the fractal characteristics of the meso-pore and crack growth morphology has good consistency with the macro-established damage variable, which can explain the freeze-thaw failure process of rocks from the perspective of meso-structure changes.