Climate change has a high chance of stimulating soil organic carbon (SOC) decomposition, thereby accelerating carbon release in soil. Alpine ecosystems sequester large amounts of SOC. However, little is known about long-term trends and future changes of SOC in alpine ecosystems. In this study, the Lund-Potsdam-Jena dynamic global vegetation model for China (LPJ-CN) was applied to simulate temporal and spatial responses of soil organic carbon density (SOCD) to climate change in Three-River Headwater (TRH) of the Tibetan Plateau from 1981 to 2100. LPJ-CN is a modified dynamical vegetation model based on Chinese terrestrial ecosystem features. Results suggest that average SOCD for the TRH in the period from 1981 to 2010 was 3.97 kg C m-2. During this period, SOCD increased at an average rate of 0.0001 kg C m-2 yr-1; spatially there was a gradient of decreasing SOCD from east to west across the TRH. Under climate change scenarios, SOCD over TRH as a whole is projected to decrease until reaching it lowest level circa 2070, and to rise thereafter. However there may be some regional variation, with SOCD increasing in west TRH and decreasing in east TRH. This decreasing trend may be enhanced further in a warming climate. However, the pattern of higher SOCD in the east and lower SOCD in the west may have less variation in the future. In general, climate warming in the future may lead to a corresponding decrease in SOCD in TRH, which may accelerate carbon release from alpine soils.