Abstract: Severe damage of alpine mountain rock slopes due to frost-thaw weathering affects road construction and safe operation. This paper is to reveal the failure mechanism of rocks under freeze-thaw conditions. It is based on the site catalog of alpine mountain rock slope, and combined with laboratory experiments and numerical simulation. A comprehensive evaluation of freeze-thaw damage mechanism of rock is presented. Indoor experiments have showed that rock strength is weakened after freezing and thawing. It is controlled by the rock texture and structure, the degree of cementation and the initial fractures. The freeze-thaw tests reveal that development of rock fractures plays a decisive role in the nature of frost heave. The freeze-thaw damage rate along the fractures is far greater than the intact rocks. The process of fissure water frozen into ice forms the split effect. The expansion force can be reach to 33MPa or greater. Numerical analysis reveals that the slope temperature field is affected by low and large temperature difference. Fractured zone is the most obvious area that is affected by freezing and thawing. It is the channel of slope freeze-thaw weathering. The congelifraction formed by fracture water frost heave is the main model of slope freeze-thaw weathering damage.