Clarifying the spatial distribution of soil organic carbon (SOC) can provide a theoretical basis for mitigating carbon emissions. The characteristics of SOC and soil organic carbon density (SOCD) change in different vegetation and soil types, and the response mechanism of SOC content to environmental factors are unclear. Thus, 131 sites were selected for sampling from the 0‒30 cm soil layer to study regional SOC and SOCD spatial distribution. The results showed that the SOCD in the northwestern region was lower than that in the southeastern in the northeast of the Qinghai-Tibet Plateaue. Both SOC and SOCD were affected by the vegetation type. The order of vegetation types was swamp > meadow > steppe > desert. Furthermore, SOC content decreased with increasing soil depth in the 0‒30 cm soil layer. The SOC and SOCD contents also differed among the different soil types. The order of SOC from largest to smallest was alpine meadow soil > bog soil > chestnut soil > saline-alkali soil > alpine steppe soil > grey-brown desert. The path analysis showed that TN significantly positively affected SOC (P < 0.001). This study aimed to provide a scientific basis for grassland carbon sink management in the Qinghai-Tibet Plateau.