The stability of high rock slope has a direct impact on the smooth construction of a hydropower station. Due to large unloading depth and developed dikes, faults and fissures, as well as large-scale excavation, a large number of cracks occurred in the excavation of the right bank slope of a hydropower station in southwest China, which would produce unfavorable influences on the subsequent construction and the stability during operation period. Based on the cracks of high rock slope and according to the geological data, monitoring results and construction conditions, the causes of cracks are analyzed comprehensively and the corresponding engineering treatment measures are suggested, which may provide references for the exploration, monitoring and engineering treatment of similar projects.