【Objective】Soil organic carbon (SOC) is a key index in estimating soil fertility and soil C sequestration. It is, therefore, important to study changes in SOC to accurate assessment of regional soil C sequestration potential and successful sustainable utilization of soil resource. This paper was oriented to characterize spatio-temporal variation of SOC, including density and storage, in the farmland of Anhui during the 30 years after the Second National Soil Survey in the 1980s and to explore relationships between agricultural management and changes in SOC, and expected to be able to provide certain data and support for decision making related to improvement of soil quality and soil C sequestration potential in the East China. 【Method】In this paper, Anhui Province in East China, was selected as a case for the study. Comparative study was done of the data obtained during the Second National Soil Survey and the data derived from the soil profiles collected from the farmland in 2010 and 2011, analyzing changes in soil organic carbon density (SOCD) in the surface layer (0 ~ 20 cm) and total layers (0 ~ 100 cm) of the farmland by means of statistics. Spatio-temporal change of soil organic carbon density and storage in the different layers during 1980 and 2010 was analyzed using the pedological professional knowledge-based (PKB) method and GIS spatial analysis technique. And then relationships between agricultural management and changes in SOC were discussed. 【Result】Results are shown as follows: (1) from 1980 to 2010, the mean of SOCD in the farmland increased by 0.28 kg m^-2 in the surface layer, but decreased by 0.42 kg m^-2 in the 0 ~ 100 cm layer in throughout the province. The increment of SOCD was higher in upland in paddy field. (2)Spatially, SOCD in the surface layer increased in the northern part, but decreased in the southern part of Anhui Province during the 30-year periods, and the increment declined from north to south within the province. SOCD in the 0 ~ 100 cm soil layer increased in the middle part and decreased in the southern part of the Province. About 68% of the farmland increased in SOCD, and the farmlands were distributed mainly in the Huaibei Plain and Jianghuai hilly downland. (3) The storage of SOC in the surface layer of the farmland of the province as a whole increased by 35.30 × 10⁹ kg and that in the 0 ~ 100 cm soil layer did 18.12 × 10⁹ kg. The storage of SOC in the farmland increased mainly in the Huaibei Plain and Jianghuai hilly downland, while it went reversely in the other geographical areas. 【Conclusion】Fertilizer application rate and straw return are the two main factors significantly influencing variation of SOC in the farmland. In this study, it was found that variation of SOC storage was significantly and positively related to organic matter content in crop roots, and that the application of large volumes of chemical fertilizers increased organic matter content in straw and roots of the crop, thus increasing the input of organic matter into the soil and contributing to accumulation of SOC in the farmland.