Abstract. Carbon sequestration of cropland has the potential to mitigate global greenhouse gas emissions. To understand such sequestration of an irrigated wheat-maize rotation cropland with high groundwater table in the North China Plain, the carbon budget and its components are estimated with a comprehensive field experiment by combining eddy covariance technique, soil respiration experiment differentiating heterotrophic and below-ground autotrophic respirations, and biometric measurements in a relatively wet year from October 2010 to October 2011. In the experimental period of a whole winter-wheat and summer-maize cycle, the Net Ecosystem Exchange, Gross Primary Productivity, Ecosystem Respiration, soil heterotrophic respiration, below-ground autotrophic respiration and above-ground autotrophic respiration are −437.9, 1078.2, 640.4, 376.8, 135.5 and 128.0 gC m⁻², respectively for wheat season, and are −238.8, 779.7, 540.8, 292.2, 115.4 and 133.2 gC m⁻², respectively for maize season. The experiment allows for estimations of Net Primary Productivity, Net Ecosystem Productivity and Net Biome Productivity. The Net Biome Productivity are 58.8 and 3.9 gC m⁻² for wheat and maize season, indicating that wheat is a carbon sink and maize is close to carbon neutral. However, compensated by the net ecosystem carbon release in two rotation periods, Net Biome Productivity of the whole wheat-maize rotation cycle is 12.8 gC m⁻² yr⁻¹ in the experimental year, indicating this cropland remains a weak carbon sink under the specific climatic conditions and field conditions with a high groundwater table. The cropland has a higher ecosystem carbon use efficiency (CUE) than other terrestrial ecosystems, indicating that the agro-ecosystem is more efficient in harvesting CO₂ from the atmosphere. This irrigated wheat-maize rotation cropland with high groundwater table has higher CUE than other croplands, implying that the cropland management of full irrigation and fertilization promotes carbon accumulation in crops.