A three-dimensional discrete element method (DEM) model was developed to explore the influences of shear direction and geogrid anisotropy on the shear strength behavior of geogrid-soil interfaces. In the DEM model, the anisotropic tensile behavior of biaxial geogrid was simulated using double-layered bonded spheres, and the irregular soil particle shapes were also considered. The DEM model for geogrid-soil interfaces subjected to shear in different directions was validated using experimental data. The tensile force development of geogrid ribs and the evolution of microstructure of the soil particles were presented and discussed. Results show that the interface shear strength in the 45° shear direction is the highest due to the passive resistance from both the longitudinal and transverse ribs. The evolution of microstructure of the soil particles indicates that the shear direction has a certain influence on the amplitude of normal contact force but little influence on the principal direction. The interface shear strength generally decreases with increasing anisotropy of biaxial geogrid due to the decrease of overall geogrid strength. The anisotropy of biaxial geogrid has an important influence on the geogrid rib passive resistance but little influence on the geogrid surface frictional resistance.