Abstract: After the pre-stressed anchor cable is reinforced, the mechanical property of slope rock mass is improved so as to lead to change of stress state. It will not be very reasonable if evaluation is made according to the normal stability of slope at this moment. Hence, in this paper, the mechanical properties of supporting structure are proposed and adopted to represent the stability of slope after reinforcement. Specifically, the difference value between the stress increment and the permissible stress increment caused by deformation of pre-stressed anchor cable under various working conditions is used, that is, the stability of slope can be indicated with the specific value of the difference value and permissible stress increment. The slope of axis of dam on the left bank of a certain hydropower station has features of high natural bank, large natural angle of repose and gneissic schistosity steep dip off the shore. Also, the steep dip crack and the flat crack perpendicular to gneissic schistosity are the main factors controlling the stability of slope. In this paper, the deformation analysis model of excavation of slope on the left bank is built through combination of site geological data, monitoring data and investigation conditions and utilization of discretization finite element software FINAL. A comparative study is made on the stability of slope of different design schemes of pre-stressed anchor cable reinforcement under three types of working conditions. The stability coefficient of slope is calculated by using the safety stability coefficient equation proposed in this paper to come to a conclusion that the working conditions of storm rainfall are the most dangerous working conditions. Then the deformation field, displacement field and stress field under the most dangerous working conditions are analyzed. The research findings have some reference value for subsequent reinforcement of the slope of the dam axis of the left bank.