Abstract: After the “6 • 1” Lushan earthquake, unstable rock mass was discovered in Zhangjiagou, posing a severe threat to the safety of the residents and their property below. The dangerous rock mass was evaluated using stability calculation and the discrete element numerical analysis method, and the seismic condition with the highest threat level was selected for kinematic analysis. Based on this research, a combination of analytical solution and numerical solution was used to design corresponding protective measures. The main conclusions are as follows : (1) The structure of the unstable rock mass in Zhangjiagou is broken, and a controlling structural plane is developed along the slope. (2) The stability calculations and numerical simulations show that the Zhangjiagou unstable rock mass will become unstable under natural, rainstorm and seismic conditions, with the longest movement distance occurring during an earthquake. (3) The failure mode of the dangerous rock mass under seismic conditions is a shatter-slip type, where the rock mainly slips during movement, and the jump height is small. Additionally, the slope shape significantly affects the characteristics of rockfall movement. (4) The collision and extrusion between rockfalls can change their motion characteristics and impact kinetic energy, potentially increasing the scope of the disaster. The research results can provide a reference for similar disaster prevention and control efforts.