Abstract: By using a professional simple shear device, the monotonic and cyclic behaviors of coarse-grained soil-steel interface are investigated. The soil deformation occurs firstly near the structural plate and then transfers far away due to monotonic shear application. The soil deformation is restrained to a localized shear zone, whose thickness is approximately 6D₅₀~7D₅₀ (mean size). The sliding displacement occurs at the starting of shearing and increases faster after the shear strength is mobilized at the sliding displacement of about 0.5D₅₀, indicating that the interface fails at the contact surface. The normal stress has a significant effect on the magnitude of soil deformation, but has little influence on its profile and the interface thickness. As for the cyclic shearing, the interface thickness remains invariable. The soil deformation presents anisotropic response since it migrates to the initial shear direction; and its amplitude decreases with shear cycles, revealing that the soil as well as the interface becomes hardened due to cyclic shear application. The mobilization of the interface shear strength mainly depends on the magnitude of sliding displacement, and after mobilized, the shear strength reduces by 16% with shear cycles and is also anisotropic.