The undisturbed regions along the Qinghai-Tibet Highway crossing the natural zones of montane desert, alpine meadow-steppe, and montane shrub-conifer-ous forest were chosen as the study areas. Soil samples were collected at 23 sites and the relations between the influ-encing factors and distribution of soil organic carbon (SOC) content were studied. The results indicated that the order of SOC content for the whole soil profile with differ-ent vegetations and in the horizontal direction was shown as below: forest > shrub > meadow > steppe > desert. All the SOC contents of the top 10 cm soil layers of forest, shrub and meadow vegetations, as well as that of the top 20 cm soil layers in steppe, in the vertical direction, were higher than those of corresponding lower soil layers. However, the SOC content in the desert soil was in accord-ance. The grey correlative analysis between the climatic factors and SOC content in the top soil show that precip-itation was the dominant climatic factor affecting the dis-tribution of SOC in the Tibetan Plateau transect. The influence of precipitation on the horizontal distribution of SOC decreased with the increase of precipitation in the horizontal direction. The vertical distribution of SOC along the soil profile was greatly affected by precipitation or the soil clay content in top soil layers, and was clearly influ-enced by soil silt content or sand content in lower soil layers, as well. The influences of both soil bulk density and soil pH on the vertical distribution of SOC along the soil profile gradually declined. The plant biomass was the most import-ant biotic factors affecting the distribution of the SOC.