Abstract: The carbon content is a metric of plant carbon storage, which reflects the ability to fix and store carbon element in photosynthesis of the green plants, is also one of important indexes to estimate carbon storage of ecosystem. The carbon contents, and their relationships with the calorific values of 67 plant species in three types from different climate zones of Xilin Gol Grassland (meddow steppe, typical steppe, desert steppe), Inner Mongolia were studied with the method of the field sampling and experimental determination, and the carbon content variation of different plant functional groups based on several classification method were studied at the same time. The aim is to provide theoretical basis for estimating scientifically carbon storage of grassland ecosystems. The results showed that the carbon content in the 67 species of plants were in normal distribution, the average value was (52.17±2.01)%, of all the species, the Salsola collina, a kind of annual forb, had the lowest value (43.79±1.37)%, and Thalictrum squarrosum, a kind of perennial forb, had the highest value (57.12±4.58) %. Among the groups classified by life forms, the order of average carbon content (%), from low to high, was: annuals and biennial plants (49.39±2.88)＜perennial fobs (52.31±1.65)＜sub-shrub (52.84±1.90) and perennial grasses (53.54±0.88). The carbon content of annuals and biennial plants were significantly lower than those of other groups (P<0.05), and there were no significant differences among the other three groups (P>0.05). The carbon contents (%) of the different plant groups based on water ecological types, followed the order: xero-mesophyte (50.01±4.36)＜mesophytes (51.80±1.92)＜wet-mesophytes (51.96±0.78)＜xerophytes (52.34±1.90) < meso-xerophytes (52.54±1.53). No statistically significant differences were found among these groups (P>0.05). Different families showed apparent difference in average carbon content (P<0.05), the lowest value was found in Chenopodiaceae, only (48.43±2.65)%. And there was a positive correlation between the carbon contents of 67 species and their calorific values (r=0.52, P<0.01).