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Rocky desertification is of extensive occurrence in karst mountain areas, particularly in the areas where pure carbonate rocks are underlying in Southwest China. Rocky desertification has great impacts on local social and economic development. This paper puts its focus on the mechanism of rocky desertification and its deterioration due to human activities. Soil creeping and sliding occur intensively in the weathering crust of carbonate rocks and at the interface between the weathering crust and the underlying bedrock. Abrupt soil-rock contact occurs at the interface is attributed to long-term soil creeping and sliding on the bedrock surface, which is usually very smooth. Both surficial and underground soil losses can cause rocky desertification in this area. In the areas where pure carbonate rocks are underlying, underground piping erosion may be the predominant process of rocky desertification because the pedogenic rate is usually lower than the rate of natural soil erosion. In general, rocky desertification is a natural, irreversible geomorphologic process in most of the karst mountain areas where pure carbonate rocks are underlying in Southwest China. Human activities often speed up rocky desertification. Present soil conservation measures, such as forestation and terracing, have little effect on the mitigation of rocky desertification. Therefore, it is a new challenge to mitigate rocky desertification in the karst mountain areas where pure carbonate rocks are underlying.