Abstract: The estimation of grassland biomass carbon is often based on large-scale spatial sampling, ignoring the community composition and spatial difference of grassland, which may affect the accuracy of assessment results. The object of this research is to reveal the above- and below-ground biomass carbon allocation pattern on community level based on the aboveground biomass (AGB) and belowground biomass (BGB). The results indicate that:(1) The temperate desert steppe contributed 120.44 Tg (1 Tg=10¹² g) biomass within an area of 35.18×10⁶ hm². 15.67 and 104.78 Tg were stored in AGB and BGB, respectively. (2) The average biomass carbon density was 406.75 g·m^-2. Nitraria tangutorum community had the highest belowground biomass carbon (BGC)(921.58±354.29) g·m^-2, while there were no significant differences in aboveground biomass carbon (AGC) (P>0.05) among communities. (3) The root:shoot ratio in temperate steppe was 4.79, while in temperate desert steppe was 6.69. (4) Distribution of BGC was divided into two types:"exponential function type" and "quadratic function type". Communities of Allium polyrhizum, Reaumuria songarica, Sarcozygium xanthoxylon, Stipa tianschanica, Stipa glareosa, Artemisia frigida, Caragana intermedia and Caragana microphylla were "exponential function type" (BGC were mainly distributed in 0-10 cm depth; the fitting curve is exponential function). Communities of Nitraria tangutorum and Haloxylon ammodendron were "quadratic function type" (BGC were mainly distributed in the depth of 0-10 and 20-40 cm; the fitting curve is quadratic function). Evaluation of grassland biomass carbon storage by different grassland communities is meaningful for understanding carbon storage dynamics and providing a theory to support natural grassland management and research in northern China.