Abstract: The K85 slope is a typical high cutting slope in the mountain of Fujian province, which is located in an expressway of Fujian province. During the slope treatment, there appeared cracking deformation and partially collapse, and formed a landslide disaster. The landslide affected the smooth opening of the line. So, for the similar slopes, it is great significance to study the deformation mechanism of this slope. In this paper, by analyzing the geological environment of the slope and the deformation of the slope excavation, the deformation and failure mechanism is described. It indicates that the deformation and failure mode is that the overlying weathered rock mass along the underlying rock surface caused the sliding deformation and damage. It uses finite element numerical simulation to analyze the steady-state of design schemes and actual construction conditions. And combining with on-site monitoring results, it confirms the deformation mechanism of these slopes. Meanwhile, it analyzes the risk prevention and control nodes about the treatment process in this kind of slope. Finally, the slope prevention and reinforcement scheme is optimized for the instability landslide. And, it is reasonable and feasible to verify the scheme by numerical simulation and new monitoring results.