The response patterns and intrinsic mechanisms controlling the distribution and accumulation of soil organic carbon and its fractions were determined under long term vegetation restoration in the southwest karst area of China. This paper aims to provide a scientific basis for the scientific management of rocky desertification in karst areas and the clarification of soil carbon sink effects during karst vegetation restoration. Seven typical restoration measures implemented in four vegetation restoration projects (Tree forest construction: Cupressus funebris and Tectona grandis planting; Shrub forest constructions: Zanthoxylum bungeanum and Hylocereus undatus planting; Vine forest construction: Lonicera japonica planting; Grassland constructions: Pennisetum sinese and Amomum villosum planting), all carried out for 28-31 years, were investigated in a typical karst rocky desertification area in the southwest China. The distribution and accumulation of soil total organic carbon (SOC), active organic carbon (AOC), slow-active organic carbon (SAC), and inert organic carbon (IOC) under long term vegetation restoration were systematically analyzed. Three main results were obtained. (1) The long term vegetation restoration in the region significantly changed the distribution and accumulation of SOC and its fractions. The construction of artificial tree and vine forests significantly improved the distribution and accumulation of SOC and its fractions. The construction of an artificial grassland not only failed to increase the accumulation of SOC, but in most cases reduced the content and storage of SOC and the content of some SOC fractions. (2) Long-term vegetation restoration in the karst region clearly affected the structure of the fractions of SOC pool. In addition to artificial grassland construction, vegetation restoration significantly increased the proportion of SAC in the SOC pool. Artificial planting of Zanthoxylum bungeanum significantly reduced the proportion of AOC in the SOC pool. Planting Cupressus funebris significantly increased the proportion of IOC in the SOC pool, while planting Hylocereus undatus and Amomum villosum significantly decreased the proportion of IOC in the SOC pool. (3) Soil total nitrogen (TN), total phosphorus (TP), and bulk density (BD) had extremely significantly positive/negative correlations with the distribution and accumulation of SOC and its fractions, and were the main factors influencing the distribution and accumulation of SOC and its fractions in the study area under long-term vegetation restoration. The results provided a theoretical basis for the science-based vegetation restoration of the fragile ecosystem of the southwest karst area of China, enabling the regulation of the soil carbon cycle based on vegetation restoration to achieve carbon neutrality.