Abstract: Through field investigation, sampling and laboratory test analysis, this paper studies the carbon reserves and constituent characteristics of six natural grassland ecosystems in Ulanqab: warm meadow grassland, warm typical grassland, temperature desert, temperature mountain meadows and temperature lowland meadows in Ulanqab. The results show that the total vegetation biomass of temperate mountain meadows, meadow grasslands, lowland meadows, warm typical grasslands, temperate desert grasslands and temperate grassland deserts from large to small: 981.795g/m², 795g/m^2, 484.11g/m², 364.03g/m², 270.48g/m², 128.21g/m², of which the root biomass accounts for 83.69%-91.72% of the total biomass. The ecosystem carbon density of temperature mountain meadows, meadows, lowland meadows, temperate typical grasslands, temperate desert grasslands, and temperate grassland deserts are 32.91Kg/m², 18.15Kg/m², 28.64Kg/m², 10.30Kg/m², 6.31Kg/m², 5.90Kg/m². The proportion of soil carbon density in the ecosystem carbon reserves is between 95.71%-98.31%. The proportion of temperature mountain meadows, lowland meadows, meadows, temperate typical grasslands, temperate desert grasslands, temperaturey deserts and warm grasslands 0 to 80cm soil organic carbon reserves are: 31.93Kg/m², 28.16Kg/m², 17.39Kg/m², 9.94Kg/m², 6.04Kg/m²,5.77Kg/m²，Soil carbon density decreases with the increase of soil depth. The total carbon reserve of natural grasslands in Ulanqab is 342.61Gt, and the carbon reserve of warm typical grasslands is 146.60Gt higher than that of other types of grasslands. Carbon reserves of different grassland types are temperate typical grassland > temperate desert grassland > temperate meadow grassland > temperate grassland desert > temperate lowland meadows > warm mountain meadows.