A large number of deep fractures have formed on the bank slopes of the Jinping First-Tier Hydropower Station, particularly on the left bank slope. These fractures have a significant impact on slope stability, underground powerhouse safety, and dam construction. Despite numerous studies conducted on their formation mechanisms and evolutionary trends, a consensus has yet to be reached. This study attempts to simulate the dynamic evolution of deep fractures during the process of valley downcutting using a self-developed continuous-discontinuous deformation analysis method. The findings indicate that changes in boundary conditions resulting from valley downcutting lead to alterations in slope stability, which in turn induce deformation towards the outside of the slope and the formation of deep tensile (or tear) fractures. Notably, when the valley is incised to an elevation ranging from 1,650 m to 1,900 m, deep fractures not only expand but also generate new fractures that interconnect with each other. The evolution of high slope configurations and the self-dynamic adjustment process of high stresses are largely driven by the boundary condition changes brought about by valley downcutting, ultimately leading to the creation of deep fractures. The research findings have significant implications for the theoretical understanding and practical mitigation strategies for deep fractures in hydropower station engineering.