Abstract: The problem of freeze-thaw damage to rocks cannot be ignored in the construction of high altitude mountain areas. The significant difference in freeze-thaw damage of rocks between sunny south-facing slopes and shady north-facing slopes,namely,the shady-sunny slope effects,poses a serious problem for rock engineering projects. Tight sandstone was selected as the research object to explore the freeze-thaw damage evolution of rocks under the shady-sunny slope effects through freeze-thaw cycle tests,based on the climatic characteristics of the shady and sunny slopes in the plateau. To this aim,the surface characteristics,physical property parameters,and meso-structure characteristics of the sandstone on shady and sunny slopes after freeze-thaw cycles were compared and analyzed. The test results show that the freeze-thaw damage degradation mode of the sunny slope sandstone is mainly particle spalling and crack expansion,while that of the shady slope sandstone is basically particle spalling. With the increase of freeze-thaw cycles,the mass and longitudinal wave velocity of the shady and sunny slope sandstones decrease at a large rate first,followed by slower rates,while the porosity increases gradually. All the sunny slope sandstones show worse physical properties than the shady slope sandstones. On the basis of the image processing technique for scanning electron microscope images,the qualitative and quantitative analyses of the freeze-thaw damage in sandstones of shady and sunny slopes can be realized at the meso-scales by using cross-sectional porosity(crack)and box dimension. The different ice-water phase transition process between shady and sunny slope sandstones is the reason for the difference in the freeze-thaw damage between them.