Water conservation as an important ecosystem function has caused a rising interests in the scientific community in recent years. Huang-Huai-Hai Plain has a substantial cultivated land area and typical cultivated land-use patterns. So, the research on water conservation function of cultivated land in this area is important for regulating the regional water resources and promoting the sustainable utilization of cultivated land. We constructed a basic research framework of the water conservation function of cultivated land in Huang-Huai-Hai Plain, which based on the dualistic water cycle process of cultivated land use systems. The water conservation function and spatial distribution of cultivated land in the Huang-Huai-Hai Plain was evaluated with cultivated land cover data, climate data, and soil data, by using the Soil Conservation Service Curve Number(SCS-CN) model. The results suggested that the water conservation function of cultivated land should be identified by the ideal water conservation ability, effective water conservation ability, and net water conservation ability, which were 1890.74×10⁸, 1127.76×10⁸, and 464.62×10⁸ m³, respectively, in Huang-Huai-Hai Plain in 2012. And the water retention function of cultivated land showed obvious spatial heterogeneity:It was strong in the northern and southeastern regions of the study area, but it was weak in the central and southwestern regions of the study area. This study provides a new perspective on research of the ecological function theory of cultivated land, and a reference and support for regulating water resources effectively and formulating ecological compensation of cultivated land.