Abstract: The shear characteristics of base material soil-rock interface are studied by means of in-situ shear tests by using the homemade shear apparatus under various interfacial roughnesses and root densities of Indigofera amblyantha. The test results reveal that the shear stress-displacement of the base material soil-rock interface is characterized by typical shear softening. Under the reinforced effect of roots on base material soil and its anchorage effect on soil-rock interface in the tests, the rooted samples exhibit rough fractured shear failure plane. The contribution of roots to improving the interfacial peak shear strength, peak shear displacement and residual shear strength is significant. According to the comparison, it is found that the contribution differences are small for the same root area ratio (RAR) to improving the intrfacial peak shear strength under different roughnesses. For a small RAR, the contribution ratio of roots is lower than that of interfacial roughness. As RAR increases, however, the effect of roots on improving the interfacial peak shear strength is more obvious, the contribution ratio of roots thus increases significantly.