The Dagangshan hydropower station’s right bank slope is located on the fault block cut by Dadu River and Moxi fractures; over there, the high intensity earthquake happened frequently; the rock mass is strongly unloaded, with poor stability structure and intensively cracks. The importance of cable support in slope excavation process has been shown in existing researches; while the design of shear hole support has been studied comprehensively by a number of scholars. Based on the existing cable supporting and unloading theory, this paper evaluates, the effect of secondary support of designing shear hole and its seismic performance simulated by pseudo-static method. And through the displacement response of key points in different elevations, the necessity of the shear hole has been demonstrated systematically. An evident cracking area has been found between cable support segment and shear hole support segment by studying the change of stress. Finally, some advises for later project monitoring are put forward.