［Objective］ The characteristics of soil carbon sequestration and its influencing factors of urban sponge green space were analyzed to provide a scientific basis to urban green spaces and urban green space planning and management. ［Methods］ Three parks in Nanning City were selected as study sites， focusing on sponge-type green spaces （rain gardens， water purification terraces， and grass swales） and conventional green spaces （multilayered tree-shrub-grass green spaces and conventional lawns）. The carbon， nitrogen， and phosphorus contents in runoff collected from the green spaces， the existing litter stock， and the soil organic carbon content in the 0—20 cm soil layer were analyzed. ［Results］ ① The ratio of catchment area to green space area and the amounts of organic carbon， nitrogen， and phosphorus inputs from runoff were greater in sponge-type green spaces than in conventional green spaces. However， there was no significant difference in litter stocks between sponge-type and conventional green spaces. There were no statistically significant differences in the natural water content， bulk density， or porosity in the 0—5 cm soil layer between sponge-type and conventional green spaces. ② Except for the natural water content in the 0—5 cm soil layer of rain gardens， which was significantly higher than that of other types of green space. ③ The average soil organic carbon content in the 0—20 cm soil layer of rain gardens and grass swales was 7.73 g/kg and 10.69 g/kg， respectively， which was 1.33 and 2.20 times that of conventional multilayered tree-shrub-grass green spaces and lawns， respectively. The soil organic carbon content of water purification terraces showed no significant difference from that of conventional multilayered green spaces. The soil organic carbon content of sponge-type green spaces increased with age of the green space. The ratio of catchment area to green space area， carbon and phosphorus content in runoff， and organic carbon content in litter were the main factors influencing soil organic carbon content in sponge-type green spaces. ［Conclusion］ Sponge-type transformation was beneficial for soil carbon sequestration in urban green spaces. The primary mechanism for increased soil carbon sequestration in sponge-type green spaces is the collection of more organic carbon through external runoff.