Abstract: With the rapid growth of the construction scale of mountainous highways, the number of high fill roadbed projects using soil rock mixed filling materials has increased. This article relies on a high fill roadbed project in Guizhou province to study the factors affecting the mechanical properties of soil rock mixtures and their impact on roadbed deformation. The results indicate that as the stone content increases, the change in cohesion of the soil rock mixture is divided into three stages: decrease, increase, and decrease, corresponding to stone contents of 0-20%, 20% -60%, and 60% -80%, respectively; the process of changing the internal friction angle is divided into three stages: increasing, decreasing, and increasing again, corresponding to stone contents of 0-40%, 40% -60%, and 60% -80%, respectively. An increase in stone content and compaction degree will significantly reduce the settlement deformation of the roadbed. When the stone content is 40% and the compaction degree is 98%, the maximum settlement is reduced by 56.5% compared to pure soil subgrade. For high fill roadbeds, it is recommended to control the compaction degree to 96% or above, with a stone content of 40%, and to use a 98% standard to control the compaction degree of fill materials in key areas. The research conclusion provides a quantitative basis for the design of fill materials for high fill roadbeds in the southwest region.