The groundwater level rises once the drainage hole of high slope is blocked during construction or operation, affecting the slope stability and safety of the supporting structure. Based on the law of seepage refraction, this paper focuses on the changes of groundwater level and the mechanical response of supporting structure in cases of different blockage conditions. The calculation results firstly demonstrate that the impact of the drainage hole blockage on pore water pressure development is significant, and that the displacement change within the slope is less obvious. Secondly the axial force along the anchor rod of the slope increases obviously with the maximum growth rate of 45%. In addition, for the high slope in the rock formation arranged with the deep drainage hole, the displacement and stress of the support structure changes significantly after the drainage hole blockage. Therefore, the impact on the supporting structure should not be ignored, especially in the position of the shear outlet on the slope toe. Safety factor of the slope decreases significantly when the drainage hole is almost completely clogged. This paper also introduces a high slope treatment method of the supporting system adopting the frame type and anchor rod, that is, for the lower part of the slope, strengthening the lattice support strength; and for the upper part of the slope, increasing the anchorage length of the anchor rod.