Identifying the carbon source/sink strength of grassland ecosystems in Xinjiang is of great importance for the regional carbon cycle. Using the modified Biome-BGC grazing model, we modeled carbon dynamics in grasslands in Xinjiang, northwest China with varying grazing intensities. In general, the regional simulation estimated that the grassland ecosystems in Xinjiang acted as a net carbon source, with a value of 0.38 Pg during the period 1979-2007, of which 0.37 Pg was caused by grazing. In general, the strength of carbon sequestration improved when grazing intensity was less than 0.24 head/hm². However, the over-compensation effect may also be the result of the growth of poisonous grass. Therefore, in the future, by adding the "vegetation succession" module, we should improve the Biome-BGC grazing model to study the compensation effect more intensively. Our findings have implications for grassland ecosystem management as they relate to carbon sequestration and climate change mitigation, e.g., removal of grazing should be considered in strategies that aim to increase terrestrial carbon sequestrations at local and regional scales. We anticipate that our study will emphasize the need for large-scale assessments of how grazing affects carbon cycling.