Abstract: There is a lot of loose Quaternary deposit originated from landslide deposits, weathering residues, slope wash and diluvial deposits etc, prevails in the Three Gorges Reservoir area. The mechanical properties of the material are widely different from homogeneous and continuous soil. To emphasize its component and structural characteristic, this special geological material is termed as "rock-soil aggregate"(RSA) in this dissertation. Based on the large number of geological investigations, the genesis types of RSA are generalized. In-situ direct-shear tests are conducted on the landslide. The deformation and failure mechanisms of RSA under shearing conditions are disclosed.