Ningde nuclear power plant in Fujian province is one of the national key construction projects of nuclear power, in order to insure the smooth progress of construction project, it needs to assess the rock slope stability which lies in the southeast of the living area. On the base of the rock architectural feature, the qualitative analysis, the three-dimensional limit equilibrium and the three-dimensional finite element are adopted to analyze the stability of the slope. The result of the qualitative analysis shows that most of the slope is stable, and part of it may fail after excavation. The result of the three-dimensional limit equilibrium and the three-dimensional finite element both illustrate that the slope is stable after excavation with slope ratio 1:0.25,1:0.50 and 1:0.75, and the stability factor rises with the decreasing of the slope ratio. At last, according to the above computing result, the 1:0.50 or the minor value is suggested to be adopted as the design slope ratio to excavate the slope.