Abstract: The periodic variation in reservoir water levels often results in decreased stability of mixed soil-rock bank slopes in reservoir areas, posing a threat to the normal operation of hydropower stations. Addressing the inadequacy of considering the content of coarse-grained soil in existing studies on macro-grained soil-mixed bank slopes, this paper takes the accumulation body of the Zhugangshan Tunnel in Tianquan County, Ya'an, as a prototype. Gravel soil samples from the reservoir area were selected, and three sets of physical model tests were designed under varying giant particle soil content. The study investigates the deformation and failure characteristics of mixed bank slopes with giant particle soil, based on variations in giant particle soil content under water storage conditions. The results indicate that the stability of the coarse-grained soil-rock mixed bank slope is sensitive to reservoir water level variations, with pronounced deformation in the initial storage cycle. The water storage deformation process of the mixed bank slope with large particles primarily involves soil softening upon water contact, surface compaction and settlement, internal erosion, particle loss, and shallow slope collapse. As the content of giant particles within the slope increases, the heterogeneity of the soil-rock mixture rises, leading to a decrease in bank slope stability. However, as the giant particle content continues to rise, particle-to-particle contact forms a relatively stable soil skeleton, further enhancing the bank slope's ability to resist deformation. When the content of giant particles increases further, the more dense the particle skeleton, the better the overall stability of the bank slope.