【Objective】Estimating the spatial-temporal changes of farmland soil organic carbon density (SOCD) provides a scientific basis for food security and double-carbon strategy.【Method】In this study, a total of 371,976 polygonal patches and 57,254 sampling sites were used to establish 1:10,000 databases. The raster dataset of soil organic matter content was interpolated using the simple kriging method combining with ancillary variables of terrain information, which was an optimal interpolation established in the earlier study based on the idea of “ideal interpolation method + efficient auxiliary variables”. Then, the SOM content was assigned to each polygonal patch of the farmland map with the help of the spatial analyst tools of ArcGIS v. 10.8 software. Eventually, the SOCD was calculated. Moreover, the gravity center migration model was employed to quantify the regional differences in farmland SOCD changes in Fujian Province from 1982 to 2018. The regions mentioned above referred to different administrative regions of nine cities, soil types of nine soil groups, three land use types of paddy fields, dry-land, and irrigated land, and two climatic zones such as the middle subtropics and south subtropics of Fujian. Also, these nine cities were divided into the southeastern coastal cities and northwest inland cities of Fujian.【Result】The farmland soils in different regions had dual functions of carbon source and sink in the past 40 years. Viewed from the area ratio of farmland soil carbon source and sink, the carbon sequestration capacity or loss intensity of most farmland was concentrated in the range of 0～1 kg?m-2, regardless of administrative regions, soil types, land use types, or climatic zones. Specifically, the farmland SOCDs in the southeastern coastal cities of Fujian were 2.37～2.65 kg?m-2 and 2.23～2.83 kg?m-2 in 1982 and 2018, respectively, which were much lower than those of northwest inland cities (2.92～3.24 kg?m-2 and 2.99～3.30 kg?m-2). It was also found that Putian was the only city to experience a decline in SOCD, with a carbon source effect of 0.31 kg?m-2. In terms of soil types and land use patterns, paddy soils and paddy fields were the most important carbon sink, with SOCD increased by 0.10 kg?m-2, while coastal solonchaks, aeolian soils, and dry-land contributed as a carbon source, with SOCD decreased by 0.23 kg?m-2, 0.22 kg?m-2 and 0.03 kg?m-2, respectively. When it came to climatic zones, the farmland soil in the middle subtropics of Fujian increased from 3.02 kg?m-2 (1982) to 3.16 kg?m-2 (2018) in SOCD, with higher SOCD level and carbon sequestration efficiency than those of south subtropics.【Conclusion】The farmland soil organic carbon pool changes varied greatly with regions in Fujian Province from 1982 to 2018. These changes might have been mainly influenced by a combination of intrinsic soil factors and external factors such as human disturbance. Thus, our work suggests that in formulating policies for farmland carbon sequestration management in Fujian in the years to come, priority should be given to the SOCD level in different regions and their change differences.