Abstract: In order to investigate the degradation of mechanical parameters and destabilization mechanism of slate slopes in cold region under freeze-thaw conditions, the cohesion and internal friction angle of the rock mass are calculated based on the generalized Hoek-Brown strength criterion through the indoor freeze-thaw cycling mechanical test, so as to modify the cohesion and internal friction angle of Bayan Obo south slope block model which has not considered the freeze-thaw damage, and to achieve the characterization of the spatial and temporal evolution of the rock mass in the south slope. Finally, numerical simulation is used to analyze the damage mechanism of the south slope under freeze-thaw effect in the main mine area of Bayan Obo Iron Ore Mine. The results show that: after 20 freeze-thaw cycles, the cohesion of siliceous slate, mica slate, carbonized slate, and faulted rock decreased by 21.64%, 22.66%, 28.09%, 28.53%, and the angle of internal friction decreased by 12.76%, 14.72%, 19.37%, 21.35%, and the stability coefficient of the south slope decreased from 1.19 to 0.92 under the freezing and thawing effect. Under the freeze-thaw effect, the stability factor of the south slope of Bayan Obo main mine gradually decreased from 1.19 to 0.92, the shear strain in the area of 1 650-1 570 m increased gradually, and finally the slide body slipped and sheared out at 1 570 m platform.