Abstract: Understanding the impacts of ecoconstruction project on grassland soil carbon storage is crucial to assess the effectiveness of the project and its role in carbon cycling of the grassland ecosystems. Using IPCC carbon budget inventory method, this paper analyzed the influence of Beijing and Tianjin Sand Source Control Project (BTSSCP) on the grassland soil carbon storage between 2000 and 2006 in Xilingol League, Inner Mongolia, and evaluated the time needed to reach the maximal soil carbon density for three management practices (i.e., sown pasture, aerial sowing pasture, and grazing exclosure). Results showed that the BTSSCP significantly increased soil carbon storage, with a carbon sequestration of 59.26×10⁴ t C from 2000 to 2006. The rate and effectiveness of soil carbon sequestration varied significantly with management practices, with the highest rate in sown pasture (0.25 t C·hm^-2·a^-1) while a greater benefit of soil carbon sequestration in the grazing exclosure (63 million yuan). Compared with other grassland vegetations, lowland meadow and temperate meadow steppe both had higher carbon sequestration rates of 0.14 t C·hm^-2·a^-1. Long time would be needed to reach the maximum soil carbon density in grassland under the three practices, yet shorter for sown pasture with average of 57.75 years.