Rock mass quality has great influence on rock slope stability. So it is very important and necessary to re-classify the rock mass and evaluate its quality correctly after excavation. Based on the unloading rock mass mechanics theory

the arch dam abutment excavated high slope of one power station is analyzed by finite element method. Comparing initial stress field with excavation stress field

the rock mass unloading degree is studied; and then the degree of rock mass quality deterioration after excavation is also gained. With the progress of excavation

areas and degree of unloading change constantly. In order to simulate the influence of dynamic unloading

the rock mass mechanical parameters are adjusted continually according to the changing areas and degree of unloading after every excavation step. And considering the effects of excavation and unloading

the rock mass quality is re-evaluated with RMR method according to the rock mass mechanical parameters after excavation. The results show that the RMR value of slope rock decreases linearly with the increase of unloading degree. On the basis of the relationship between RMR value and unloading degree

considering unloading as an important influential factor

the evaluating parameters of the RMR method are revised

which has referential value for rock mass quality evaluation after excavation.