Abstract: Abstract: Food security always attracts strong attention from researchers and policy makers in China, because it has more than one fifth of the world's population, but the total cultivated area accounts for only about seven percent of the world's total cultivated area. However, relevant studies were normally conducted at the national level, which generally considered China's food security as a whole or used a single index system set for analysis. Therefore, study on food security from a regional scale will be of great value for policy makers. Grain production guarantee capacity of regional cultivated land is the satisfaction degree of regional grain supply to meet the national grain demand, which is mainly influenced by local cultivated land resources, cropping systems, and socio-economic factors. Regional total grain demand should be measured from a national perspective because of the mobility of grain and population; more specifically, it should be calculated based on the proportion of regional resource endowments in the national total endowments. In this paper, a framework is proposed to evaluate regional grain production capacity and the corresponding security level, and the Grey System Model is used to estimate regional grain production capacity under three different scenarios (normal harvest years, bad harvest years, and good harvest years) based on the historical grain production levels. After that, scenarios are selected that could meet the national grain demand and divide the risks of grain production guarantee capacity into four grades, i.e., low risk, small risk, medium risk, and high risk. To test this approach, the Dongting Lake area (located in the northeastern part of Hunan province) was chosen as the case study area, and 2020 was selected as the predicted year. The results show that the risk level of grain production guarantee capacity of the Dongting Lake area is low risk under normal conditions, which means the grain production capacity of the Dongting Lake area can meet the national grain demand in bad harvest years. Judging from the spatial distribution, the areas closer to the lake have a higher risk grade than the other areas. This is partly because the areas are rich in water resources so some farmers tend to give up grain planting in favor of fishpond operations, which makes cultivated land decrease. On the other hand, because of the geographic location of this area, some accidental factors, such as the natural climate, have great influence on grain yield and exhibit considerable variation, which also causes the gap among grain production guarantee capacities to increase at different times. These condition results in a relative high risk of grain production guarantee capacity in this area.On the whole, the grain production guarantee capacity of the Dongting Lake area is optimistic in the near future, but the risks of grain production guarantee capacity of some counties are high. Therefore, relevant policies should be put forward to improve this situation. The method proposed in this paper can provide a novel way to study the relationship between the grain security situation and cultivated land resources in different areas.