Abstract: Most natural slopes are composed of soil-rock mixtures, whose large deformation and failure pose severe threats to human safety and infrastructure. To overcome the challenges in high-fidelity modeling and coupled soil-rock mixture interaction analysis, this study develops a high-fidelity 3D modeling technique for soil-rock mixture slopes and proposes an SPH-DEM coupling method to simulate the large deformations. We further analyze the impact of boulders on the deformation and failure process of the slope and predict the variation of the impact on dam appurtenant structures after the reactivation of the Langjia landslide in Qinghai Province. The results reveal that boulders within the landslide body significantly increasing the landslide velocity, and the content and position of the boulders affect the impact process. Higher boulder content leads to a more pronounced difference in the impact force time-history curve. When boulders collide directly with buildings, the peak impact force increases by about 30% compared to scenarios without boulders. After reactivation, the maximum movement distance of the front edge of the Langjia landslide in Qinghai Province reaches 108 meters, with peak impact forces on the intake and construction camp structures reaching 20 times and 4 times their own weight, respectively, making them highly vulnerable to destruction by the landslide. The findings of this study provide valuable insights for disaster prediction and risk analysis of soil-rock mixture landslides.