[Objective] Studying the soil carbon sequestration characteristics of urban sponge green spaces can provide a scientific basis for understanding urban green space carbon sequestration and guiding its planning and management. [Methods]In this study，the sponge green spaces (encompassing three forms：rain gardens，water purification terraces，and grass swales) and conventional green spaces (comprising two forms：conventional multi-strata green spaces with trees，shrubs and grasses，and conventional lawns) in three parks in Nanning were selected as the research targets. The contents of carbon，nitrogen and phosphorus in the runoff collected by each form of the two major categories of green spaces，the standing stock of green space litter，and the soil organic carbon content in the 0－20 cm soil layer were analyzed. [Results]① The ratio of the catchment area to the green space area，as well as the amounts of organic carbon，nitrogen and phosphorus introduced via runoff in the sponge green spaces，were all greater than those in the conventional green spaces. There was no significant disparity in the standing stock of litter between the sponge green spaces and the conventional green spaces. ② With the exception that the natural water content in the 0-5 cm soil layer of the rain gardens was markedly higher than that of other forms of green spaces，there were no significant differences in the natural water content，bulk density and porosity of the 0－5 cm soil layer between each form of the sponge green spaces and the conventional green spaces. ③ The average soil organic carbon contents in the 0－20 cm soil layer of the rain gardens and grass swales were 7.73 g/kg and 10.69 g/kg respectively，which were 1.33-fold and 2.20-fold those of the conventional multi-strata green spaces with trees，shrubs and grasses and the conventional lawns respectively. There was no significant difference between the water purification terraces and the conventional multi-strata green spaces with trees，shrubs and grasses. The soil organic carbon content in the sponge green spaces exhibited a continuously ascending trend with the elongation of the construction years. The ratio of the catchment area to the green space area，the contents of carbon and phosphorus in the runoff，and the organic carbon content in the litter were the principal influencing factors for the soil organic carbon content in the sponge green spaces.[Conclusion] The sponge transformation is conducive to soil carbon sequestration in urban green spaces. The aggregation of more organic carbon through the influx of external runoff represents the main mechanism for the augmentation of soil carbon sinks in the sponge green spaces.