【Objective】Karst is a landscape formed through dissolution of soluble rocks, including limestone, dolomite and gypsum and characterized by a double-layer structure of surface and underground spaces. This special double layer space structure is the key factor causing development of rocky desertification in karst regions. The non-uniform surface micro-landforms and unique underground hydrogeology in the karst regions complicates the process of soil erosion. As a result, large tracts of bedrocks pop out of the land discontinuing the soil cover, while fissures, ponors, cavities and underground drainage systems are formed underground through dissolution of carbonatite. As large volumes flow through fissures and ponors into underground rivers, water and soil loss in karst regions exists in two forms, surface loss and underground loss, which obviously differ from that in non-karst regions. Guizhou Province, China is one of the largest areas in the world’s wet climate zone concentratedly distributed with karst. It has a total of 109,084 km² of karst, which accounts for 73% of the total area of the province, moreover, about 17.42% of the karst landforms are developed from a large continuous tract of limestone. Under the interaction of natural factors (rainfall, and geology and relief) and human activities, soil erosion in this region is very severe. In recent years, the unique form of underground soil and water loss in the process of karst rocky desertification has aroused more and more concern, but so far little has been reported on the underground soil erosion in karst areas different in rocky desertification degree, and the studies that have been done failed to illustrate either contribution rates of surface and underground soil losses to the total of the area or driving forces and mechanism of karst rocky desertification in the Karst region. Therefore, this study is oriented to determining and analyzing sediment generating process with surface and underground erosion in bare karst areas during the process of karst rocky desertification, and further to exploring effects of outcropping bed rock on soil erosion and effects of soil loss on development of karst rocky desertification. 【Method】For that end, a simulated rainfall experiment was carried out to explore sediment yielding characteristics of surface and underground erosion on bare karst slopes different in rocky desertification degree, by simulating their surface micro topographies and structural characteristics of underground pores and fissures. 【Result】Results show that on bare slopes with no rocky desertification, potential rocky desertification and light rocky desertification, sediment yield was generally higher on the surface than underground when other conditions were the same, and the underground sediment yield varied in the range of 0~100 g in during the initial10 min of rainfall. On bare karst slopes different in rocky desertification strength, both surface and underground sediment yields increased with increasing rainfall intensity. Under rainfalls 30 mm h^-1 ~ 80 mm h^-1 in intensity, the more intense the rocky desertification, the harder for surface erosion to occur, and on slopes with rock desertification reaching a certain degree (40% in bed rock outcropping rate), soil erosion became dominated by underground soil loss; under rainfalls 150 mm h^-1in intensity, surface sediment yield and its contribution rate did not change much with increasing bedrock outcropping rate, while underground sediment yield first increased and then decreased, and peaked on slopes 30% in bedrock outcropping rate. On bare karst slopes, regardless of rocky desertification degree, surface sediment yield and its contribution rate did not vary much while underground sediment yield and its contribution rate increased with increasing underground porosity or fissure density; on slopes 1%~5% in underground porosity or fissure density, surface and underground sediment yields and their respective contribution rates varied sharply with changes in bedrock outcropping rate in the range of 10%~50%. 【Conclusion】All these findings in this study demonstrate that they have some important theoretical and practical significance to understanding mechanism of the development of rocky desertification, revealing characteristics of the soil erosion and controlling surface and underground soil and water losses in Karst regions.