Due to specific geological conditions, stability of complex high slopes has become one of the key technical problems in hydroelectric project. Especially for steep-high rock slope, it is hard to calculate the stability by normal rigid limit equilibrium method. Steep-high rock slope in Jiangping River hydropower station is taken for example. On the base of study of geological structure and judgment of preferred structure plane, simplified geological model is built up. The main deformation destruction mode and type are analyzed based on block theory, rock mechanics and other basic mechanics while the related critical values are calculated. So slope stability is discussed and corresponding control measures are worked out. This method can be used in following stability research of similar slope.