Abstract：As a microcrystalline material，the fine crystal and special structure of clay minerals make the aggregation-clay present several important properties，such as low permeability，high viscosity，high cation exchange capacity，dispersion-flocculation and so on. Many sedimentary rocks contain clay minerals and 76% of forming-rock minerals of slope rocks can produce clay minerals during the weathering processes. Clay minerals distribute extensively in various slopes made of sedimentary rock，weathering profiles of igneous rock，metamorphic rock and sedimentary rock and colluvial deposits. Because of clay minerals，lutites fail easily，and the sensitivity of their strength and deformability to change in water content is high. Secondary clay minerals in rock may bring about marked changes in strength and deformability of parent minerals，mineral aggregation and rock and promote rock to evolve toward loose medium. Macro discontinuities are the main forming and assembling places of clay minerals，and the illuviation of secondary clay minerals in fracture surface and the rock inside fracture surface will cause the strength of discontinuities and rock mass to decrease. Clay minerals are key components of slipping zones of landslides. Slipping zones have a lubrication effect between landslide masses and bedrock. The higher the content of clay minerals in slipping zones is，the more remarkable the lubrication effect is. Slipping zones may act as impervious boundaries and separate landslide masses from the surrounding media. Thus landslide masses are changed into independent hydrogeological units，and the ability of retaining infiltrated water and sensitivity of slope stability to raining processes are raised correspondingly. To sum up，clay minerals may accelerate time-dependent deformation of slopes，and their contribution to slope evolution and failure of slopes is notable.
