Grassland soil is a large organic carbon reservoir,and a slight change in soil organic carbon (SOC) stocks has a considerable effect on atmospheric CO_2 concentration,which contributes to climate warming. A comprehensive assessment on SOC dynamics and their susceptibility to climate change in Inner Mongolia grassland is still lacking. Based on the climatic interpolation data from 92 meteorological stations over Inner Mongolia and surrounding areas,the spatial distribution of topsoil (0-20 cm) organic carbon storage in Inner Mongolia grassland and its dynamics during 1981-2010 were estimated using the CENTURY-based modeling system (complying CENTURY model from a site-based model into a spatial model). The sensitivity to climate change was also examined based on scenario simulation analysis. The results showed that the spatial distribution of SOC density (SOCD) in Inner Mongolia grassland showed a decreasing trend from the northeast to the southwest,with an average density of 1. 99 kg/m~2. Inner Mongolia grassland SOCD significantly increased over the past three decades,with an annual increase of 0. 22%, while SOCD also showed a marked heterogeneity corresponding to grassland types,with the largest increase rate of 14. 25 g/(m~2·a) in meadow steppe and the least rate (1. 36 g/(m~2·a)) in desert steppe. There was also a large decadal variability in SOCD. From the 1980s to the 1990s,it changed very slowly, while it was shown to change greatly from the 1990s to the 2000s,about twice as much as the former,primarily attributed to changes in meadow steppe and typical steppe. At the regional scale,change in precipitation played a critical role in the increase of SOCD,but its relative role was not constant across the study area. Increase in SOCD over the typical steppe and meadow steppe was primarily attributed to precipitation changes,while rising temperature was the main cause of SOCD increase in desert steppe.