Abstract: The stability and reliability of filling embankment slope is a both prerequisite and key factor for the successful construction of highways. Gravel soil, as a high-quality filling geomaterial, is commonly used for embankment construction. In this study, the mechanical behaviors of reconstituted gravels soil are investigated through large-scale triaxial shear tests. Based on the test results, the strain localization characteristics of gravel soil is studied from the perspective of meso-structure through numerical plane strain tests. Moreover, the failure patterns and stability of gravelly embankment slopes along the Linzi-Linyi Expressway are numerically explored by adopting the strength reduction method. The results show that: the by-pass effect of gravels changes the propagation of the failure path in soil matrix, and the presence of gravels in soil is able to improve the soil structure. Generally, the gravel soil is denser, and is able to bear higher external loading, compared with the same volume of homogeneous soil, thereby enhancing the stability of the filling embankment slope. Notably, the influence of gravels on the mechanical and deformation properties of gravel soil is not linear but characterized by a threshold effect, i.e., 30% gravel content.