Abstract: The problem of a deposit slope is encountered in construction of hydropower projects in Southwest China. The study combines geology phenomena and drill core data, bases on site geology survey, historical seism, rainfall data, and so on. The thought of engineering geology qualitative analysis and back-analysis is applied to study the slope stability. The results show that the slope is stable. The formation mechanism for deposit slope is as follows: on account of joints and weathering, the dip direction of top stratums is opposite to the slope, which results in toppling and falling. After rock failure, the cracked rock masses rolled and accumulated. Durative depositing, rainwater infiltration, and the geology environmental disturbance brought on deposits' concretion and compacting. Aiming at spatial structure features of deposits slope, the quantitative analysis is adopted to compute factors of the whole and partial stability under natural conditions. The possible failure patterns depending on the spatial structure features of the slope are analyzed. The whole slide is along the interface between deposits and bedrocks, and internal partial arc slide. The above discussions offer reasonable evidence to constructions of the project and partial reinforcements of the slope.