Grassland ecosystem, an important component of terrestrial ecosystem, plays an essential role in global carbon cycle and balance. The Stipa breviflora desert steppe of Inner Mongolia is a transitional ecosystem from grassland to desert, which has infertile soil, weak stability, but high sensitivity to climate and environmental changes. Study on organic carbon storage of the steppe under different grazing intensities is very important for revealing the mechanism of grazing impact on carbon process of the desert steppe and can provide theoretical basis for reasonable conservation and utilization of grassland resources. According to the grassland plant species composition, community height, coverage, aboveground biomass, and density index, the steppe was divided into plots that were subjected to three grazing intensities, heavy grazing (HG), moderate grazing (MG), and light grazing (LG), and the experimental grassland which was fenced to exclude livestock grazing in 2008 was selected as the control sample (CK). The analyses of the aboveground biomass, litter, belowground biomass, soil organic carbon, and soil light fraction organic carbon were utilized to study the organic carbon storage properties in Stipa breviflora desert steppe vegetation soil systems under different grazing intensities. The results showed the following. The carbon storage was 11.98-44.51 g/m² in aboveground biomass, 10.43-36.12 g/m² in litter, and 502.30-804.31 g/m² in belowground biomass (0-40 cm); it was significantly higher in CK than in MG and HG. The carbon storage in the soil at a depth of 0-40 cm was 7817.43-9694.16 g/m², and it was significantly higher in LG than in CK and HG. The total carbon storage in the vegetation-soil system was 8342.14-10494.80 g/m² under different grazing intensities; it was the largest in LG, followed by MG, CK, and HG. About 90.54%-93.71% of the total carbon was reserved in soil. Light and moderate grazing intensities increased organic carbon level of the ecosystem due to the increase in the root:shoot ratio. The grazing intensities of plant root:shoot ratios decreased from HD (41.94) to MD (30.24), LD (24.33), and CK (18.07), thereby increasing the allocation of carbon amount into the ground. Increased organic carbon content in the ecosystem may also be due to animals trampling and breaking the litter and thus promoting litter decomposition and carbon and nutrients release into the soil. However, heavy grazing severely reduced the grassland vegetation leaf area and storage material, decreased plant net primary production, lowered material input to levels below the output, and decreased the ecosystem carbon storage. Each component of the system accounted for the percentage of ecosystem organic carbon storage in the following order: soil > root > aboveground vegetation > litter in different grazing intensities. Organic carbon storage accumulation in the vegetation had a short-term effect, while its accumulation in the soil was relatively slow. With increasing grazing intensity, aboveground vegetation, litter, and root organic carbon storage showed a decreasing trend, while soil organic carbon storage first increased and then decreased; MG was beneficial to the accumulation of soil organic carbon storage. The soil light fraction organic carbon storage was 484.20-654.62 g/m², and it was the highest in LG. With increasing grazing intensity, the soil light fraction organic carbon content, storage, and percentage of soil organic carbon storage first increased and then decreased, reaching the highest value in LG. MG intensity was beneficial to soil nutrient accumulation in the desert steppe.