This study aimed to explore the response patterns of soil organic carbon (SOC) and its fractions to different vegetation restoration types in karst regions, so as to provide theoretical support for the stable maintenance of soil carbon pools and ecological restoration in karst areas. Based on a long-term fixed-position controlled experiment, four vegetation types including grassland, shrubland, woodland and cornfield were selected in the Huanjiang karst region to analyze the effects of vegetation restoration on particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). Compared with cornfields, the total SOC concentrations of grassland, shrubland and woodland increased by 80%, 1.2 times and 60%, respectively. The POC concentrations of grassland and shrubland were significantly higher than those of cornfields, with increments of 1.3 times and 1.7 times correspondingly, while the MAOC concentrations of shrubland and woodland were significantly elevated by 60%. The concentrations of various calcium (Ca) forms and nitrogen (N) nutrients increased markedly across successive vegetation restoration stages. Relative importance analysis revealed that the key soil physicochemical factors driving variations in POC concentration were TN, Ca(Na2SO4), N/P ratio, Ca and NO3--N. TN was the dominant explanatory factor with an importance contribution of 7.53%, followed by Ca(Na2SO4), N/P ratio, Ca and NO3--N, which contributed 5.61%, 4.91%, 4.86% and 4.72% of the total importance, respectively. For MAOC, NO3--N was also the primary influencing factor with a contribution of 6.15%, followed by Ca, TN, N/P ratio, pH, AP and C/P ratio, contributing 5.69%, 5.68%, 5.63%, 5.63%, 4.92% and 4.83% in turn. These results demonstrated that nitrogen nutrients and calcium concentrations jointly regulate SOC dynamics and play a critical role during vegetation restoration in karst ecosystems. This study verifies that promoting vegetation restoration in karst regions is an effective approach to improve soil carbon sequestration potential and enhance ecosystem stability. Meanwhile, it provides a scientific basis for karst ecological restoration and soil carbon sink enhancement based on the collaborative regulation of calcium and nitrogen.