Abstract:Based on the past researches, an initial study on the carbon cycle of Leymus chinensis (Trin.) Tzvel. steppe in the Xilin river basin of Neimenggu (Inner Mongolia) was conducted by combining field surveys and the CENTURY model simulation. The major results were summarized as follows: 1) Observed annual amount of carbon fixation via primary production for a L. chinensis community on a fenced site in the basin averaged (231.25 + 74.41 ) g C·m-2·a-1, average annual carbon input into soil was about 220.75 g C· m- 2· a- 1, while carbon output from the community via soil respiration was estimated to be (181.03 + 46.32) g C· m-2· a-1 by CENTURY model simulation; 2) The community had a simulated net carbon gain of about 19.88 g C·m-2·a-1 and an observed carbon gain of 39.72 g C·m-2·a-1; 3) About 12.4% of carbon originally stored in soil had been lost due to over-grazing over the recent 40-year period in Leymus chinensis steppe in the Xilin river basin.