Abstract: The results of slope stability are closely related with the selection of mechanical parameters of rock mass in the process of open-pit slope stability calculation and evaluation. With the increase of freezing-thawing cycles, the physical and mechanical characteristics of rock change under freezing-thawing condition. Based on experimental research on simulating natural conditions of Tibetan area, two kinds of sandstone samples were collected from different freezing-thawing cycles, then a series of uniaxial and triaxial compression tests were conducted after different freezing-thawing cycles (0, 30, 60, 90, 120 times), the physical and mechanical characteristics of sandstone were obtained. Based on the disturbance parameter D, the freezing-thawing deterioration parameter D_f was proposed. Based on the modified Hoek-brown strength criterion, the mechanical parameters of the rock mass were obtained after different freeze-thaw cycles. The failure mode of rock slope was analyzed. The results showed that with the increase of the number of freezing-thawing cycles, uniaxial compressive strength, elastic modulus and cohesion decreased, the internal friction angle changed little. However, the uniaxial compressive strength, tensile strength, the global strength, modulus of deformation, cohesion and internal friction angle of rock mass decreased; the failure form of the open-pit slope under freeze-thaw condition are shear failure. The modified rock mechanical parameters provide more accurate data for slope stability analysis of open pit.