Abstract: River incision is an important geological force for geomorphic evolution of deep valley. River incision and side erosion processes often influence the stability state and slope evolution of the slope on both sides of the valley. At present, little research results are available on the spatial distribution characteristics of slope rock mass and their quantitative relationship under the action of river incision. To some extent, this restricts the development of stability prediction of slope rock mass and susceptibility assessment of geological hazards in deep valley area. Based on the above background, this paper studies the spatial distribution characteristics of channel steepness index(k_sn) and rock mass quality index in the study area. It uses on-site investigation, statistics, Matlab, Topotoolbox, ArcGIS, Origin and other tools and examines the BQ system of rock mass quality evaluation, the river hydraulic erosion model, the relavant relationships and internal mechanisms in the deep-cut valley area(Lancang-Jinsha River) and G214 Zuogong-Tiger Leaping Gorge section of the Qinghai-Tibet Plateau. The results show that the Pearson correlation coefficients of rock mass with fracture density, k_sn and engineering rock group are 0.52, 0.67 and-0.11 respectively. The correlation degree between rock mass quality and k_sn is the highest. Based on the shape extraction of cross section and analysis of stress characteristic area of valley slope, it is found that the characteristic distribution area of rock mass studied in this paper is mainly the slope section which responds sensitively to river downcutting in real time, i.e. the section strongly affected by river incision. Based on the research results, this paper suggests that k_sn should be considered and used as an important evaluation index in evaluating the susceptibility of collapse disasters by characterizing river incision.