Rocky desertification is a major kind of land desertification. The degradation land of karst rocky desertification is one of the most serious problems on economic development, ecosystem restoration and reconstruction in Southwest China. Grassland is one of the main vegetation types in karst region of Guizhou, its root is sensitive to the response of to environmental conditions, which determines the growth and development of plants and soil nutrition status. Root dynamics also has an indicator effect on environmental changes, and can reflect the health status of grassland ecosystem. As the intermediary connecting the aboveground and underground parts of vegetation, root plays an important role in the matter exchange and energy transfer between plants and soil, root decomposition and turnover contributes significantly to element cycling in grassland ecosystems. In order to identify the root dynamics and their response to rocky desertification in different grasslands in the karst region, this paper took three different rocky desertification grasslands (potential rocky desertification grasslands, moderate rocky desertification grasslands, and intensity rocky desertification grasslands) as research objects. The continuous soil drilling method and root bag method were used to investigate the monthly root dynamic, root production and turnover from March 2017 to January 2018. The results show that the root biomass of the three rocky desertification grasslands decreased gradually with the depth of soil, root biomass in the 0-10 cm soil layer accounted for more than 57% of the total biomass in the 0-30 cm soil layer. The root biomass of potential and medium rocky desertification grasslands showed significantly seasonal variation of single-peak, and the root biomass of the severely rocky desertification grassland was not significant. The root decomposition rate all showed the ″fast-slow-fast″ status, was significantly influenced by soil organic carbon, total potassium, total nitrogen, soil water content, soil electrical conductivity, soil temperature in the three rocky desertification grasslands. When the complete decomposition rate reached 95%, 1174, 1351 and 1878 days were needed in the three grasslands, respectively. With the intensifying of rocky desertification, the root turnover rate decreased gradually, and were 1.70 times/year, 1.36 times/year, and 0.87 times/year in the three grasslands, respectively. The above conclusions provide an important scientific basis for a deeper understanding of the nutrient cycle, soil fertility maintaining and the restoration of rocky desertification grasslands. It is necessary to strengthen the research on the nutrient release mechanism of the root in rocky desertification grassland in Southwest China.