On the background of a mountainous area highway cut slope engineering, a plane strain finite element model is built by PLAXIS with its embedded strength reduction method for stability analysis.Firstly, the slope stability under excavation and reinforcement is analyzed according to the exposed stratigraphic, indicating that global stability requirement will be satisfied with frame anchor reinforcing the first two stage slopes. Secondly, after some studies it can be seen that overlying weathering layer thickness which significantly affects slope stability, a major research object for optimized design. Finally, the effect of the strength parameter c、φ, of strongly weathered layer and moderately weathered layer, on the slope stability is calculated using the built-in parameter sensitivity function of PLAXIS, which shows that c value of the strongly weathered layer has the most apparent influence on the result.