The excavation and unloading deformation stability of the deep discharge tunnel inlet at a hydropower station were analyzed to optimize the anchorage angle using software ADINA in association with the actual geological conditions and the actual needs of deformation control. Moreover, the reinforcement effect of the slope under different anchorage forces and angles was analyzed. Results show that the reinforcement effect is the best when anchorage angle of depression is 20°, and anchoring force is inversely proportional to the slope deformation. In this paper, prestressed anchor of 2 000 kN was used to control the cost. Besides, radial gate is adopted at the vertical segment of the excavated slope of deep discharge tunnel, so the deformation at this position needs to be stringently controlled to guarantee the gate’s normal operation. Anchorage force has direct influence on the reinforcement effect. The research results offer reference for the anchorage design of high and steep slopes.