Agricultural soils hold potential for the expansion of carbon sequestration. With this in mind, we investigated changes in the soil organic carbon (SOC) on the basis of an analysis of data sets extracted from 146 publications and further projected the SOC sequestration potential in China's cropland. Our results suggest that a significant increase in the SOC occurred in east and north China, while a decrease appeared in northeast China. As a whole, the organic carbon density in the topsoil to 30 cm depth increased by 3.36 (2.54 to 4.26) Mg/ha between 1980 and 2000. Accordingly, the croplands in China that cover an area of over 130 Mha sequestered 437 (331 to 555) Tg C, with an average rate of 21.9 (16.6 to 27.8) Tg/yr, during this period. The potential of SOC sequestration in China was estimated to be 2–2.5 Pg C, which could be achieved by the 2050s if crop production and field management are improved.