Combined with the methods of in situ survey, high precision testing of physical water parameters of rock blocks and laboratory tests, the CWRI （chemical water rock interaction） in silicate rock slopes was investigated. The results show that fresh silicate rock blocks are generally impervious media because of their compact texture, low porosity and very fine pore throats. The CWRI in silicate rock slopes occurs mainly in unsaturated and water table fluctuation zones, and the CWRI in the saturated zones below the lowest groundwater level is weak. The CWRI in the saturated zones only takes place in the surface of rock blocks and is a slow dissolution process in which fracture width becomes wider and wider and rock blocks become smaller and smaller. The solvent in preliminary stage of the CWRI in unsaturated and water table fluctuation zones is mainly condensation water from moistur. The saprolite deriving from the CWRI in unsaturated and water table fluctuation zones retains the relic texture, structure and volume of the parent roc. In dry season, the gaseous water molecules in unsaturated zone spread into the pore system of silicate rock blocks at some depth and condense into liquid water which can dissolve forming mineral. In rainy season, the thin water films derived from precipitation on the surface of rock blocks in unsaturated zone absorb the dissolution components in the rock block solution and carry them into saturated zone. When the above process circulates to some extent, the silicate rock blocks turn into saprolite. The silicate rock slope covered by residual soil layer and vegetation is propitious to occurrence of CWRI.