Abstract: The slope of spillway of Wudongde Hydropower Station is a toppling rock slope with a height of 150m. The slope is composed of thin layered meta-dolomite rock mass from Mesoproterozoic YinMin Formation, cleavage develops between the layers and attach sericite film along bedding plane. Rock mass integrity is poor, and rock mass quality is mainly IV level. In view of this, this paper studies the rock mass from the view of engineering geology based on the combination of mineral chemical analysis and field physico-mechanical test, such as lithology characteristics, structure characteristics and mechanical property. This paper analyzes the deformation model and evaluates the stability of the slope according to the results, and provides a basis for the design. Monitoring results illustrate the effectiveness of the support measures and the importance of timely support. The research has important value to the stability analysis of slope composed of special geological body.