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The soil organic carbon (SOC) of grasslands is a vital component of the global carbon cycle. The SOC in grassland ecosystems in arid and semi-arid regions is sensitive to global climate change, but the dynamic drivers of the SOC content are still controversial. Grazing is the main factor affecting SOC contents in grasslands; however, the response of different types of grasslands to the grazing intensity remains unclear. Based on the Denitrification-Decomposition model and field investigations, in this study, the spatial and temporal dynamics of SOC and its drivers in the grasslands in Northern Xinjiang were investigated, and the response of the SOC in the different types of grasslands to various grazing intensities at the regional scale. The results reveal that the SOC content of the grasslands in Northern Xinjiang increased at a rate of 161.32 kg C ha−1 yr−1 from 2001 to 2020, and the spatial distribution of the SOC dynamics varied greatly. There was an increasing trend at higher elevations and a decreasing trend at lower elevations. Grazing contributed less to the SOC dynamics, and temperature and precipitation were the main drivers of the SOC dynamics. The overall effect of the grazing intensity on SOC content was negative. The responses of the different types of grassland to the grazing intensity varied greatly, with the least effect in alpine meadows and the greatest effect in lowland meadows and temperate desert grasslands.