The Dagangshan hydropower station dam abutment slope stability has been studied based on the theory of unloading rock mass. Based on the large-scale universal finite element program ADINA

for the conditions of different earthquake accelerations

different anchoring lengths and tonnages of unloading dam abutment slope

the displacements of key points

stresses and plastic zones change rule are comparatively analyzed; and it is pointed out that the slope deformations are composed of two parts; one part is unloading rebound

the other part is the compressive deformation of inner facing slope induced by applying large tonnage anchors. Research shows that because of the cable through the V-shaped rock bottom line

in the possible shear zone of landslide there formed a strong resistance sliding key

so that increasing cable length or tonnage can effectively reduce the plastic zone of the abutment; for accelerations of 0.1g and 0.15g in the earthquake

in different reinforcements of tonnages

may form transfixion of plastic zone. Under different earthquake accelerations effected by different anchorage length and anchoring force

the horizontal displacements of different key points presented linearly and nonlinearly changing; inflection point in the nonlinear relationship should be paid attention to. To reduce the plastic zone of rock mass

it is better to increase anchorage length in the same proportion. In order to effectively reduce the plastic zone development during strong earthquake

the 120% increase in anchor length is suggested.