Ago-ecosystem plays an important role in terrestrial carbon cycling. Soil carbon sequestration in cropland can not only offset fossil fuel emissions but also contributes to food security. Though the evaluation of soil carbon sequestration potentials has attracted attentions worldwide, large uncertainties in estimating C sequestration potential on regional/national or global scales remain a big problem due to various interpretations of the “potential” among scientists. The paper reviewed up-to-date interpretations of “soil carbon sequestration potential” and the methods of estimating C sequestration potential in agricultural soils. Carbon sequestration potential, conceptually the maximum capacity of soil′s holding carbon or the level of SOC (Soil Organic Carbon) saturation and stability, is usually vulnerable to climate, soil characteristics and agricultural practices. Reliable estimations of soil carbon sequestration potential should therefore integrate the influence of climate, soil structure/texture and field management as well as the coupling of macroscopic and microcosmic processes of carbon turnover in soils. An integrated methodology for estimating regional soil C sequestration potential was proposed in the paper with two concepts of biological and physicochemical potentials. Key issues and prospects on soil carbon sequestration in Chinese croplands were also addressed.