The types and the current distributed characteristics of rocky desertification were analyzed, specifically explored the causes and forming mechanism of karst eco environmental fragility from the following aspects such as weathering resistance of carbonate rock,the soil forming process of carbonate rock,surface structures of karst landforms, two different kinds of boundary face in karst soil profile, overloaded pressure of population and backward farming methods, etc.Based on the analysis, eco economic model of controlling rocky desertification from three levels of production (technology), ecological (vegetation rehabilitation), lives and rural industrial development and five proposals to harness rocky desertification were suggested according to the concrete conditions of Guizhou karst mountainous regions.