Abstract: Food security never fails to attract high attention of researchers and policy makers, especially in China, which has more than one fifth of the world's population, but where the total cultivated area accounts for only about seven percent of the world's total cultivated area. However, thus far, relevant studies were normally conducted at the national level, which generally considered China's food security as a whole or used a single set of index system for analysis. Therefore, study on food security from a regional scale will be of great value for policy makers. This paper mainly focuses on the risk sources which can cause food insecurity in China. We proposed a series of supply-demand estimation models to evaluate the gap between supply and demand of food in different areas (food output areas, food import areas and food supply-demand balance areas). Based on different demand-supply gap ratios, the food security risks are categorized into four grades: negligible risk, low risk, medium risk, and high risk. After that, a case study was conducted in the Dongting Lake area. We analyzed the impact of natural disasters under different scenarios (general scenario, pessimistic scenario and optimistic scenario), use Cobb-Douglas stochastic frontier model to predict resources constraint and inputs constraint on food supply, and evaluate the future food security risk under different scenarios. The results show that if annual grain shortfalls caused by natural disasters at the historical average level, there will be 2, 2 and 4 counties/cities at the low-risk range, medium-risk range and high-risk range in 2015, respectively; and the number of counties/cities at the medium-risk range will increase to 3 by 2020. If annual grain shortfalls caused by natural disasters at the historical worst level, there will be 2, 5 and 7 counties/cities at the low-risk range, medium-risk range and high-risk range in 2015, respectively; and the number of counties/cities at the high-risk range will increase to 9 by 2020. If annual grain shortfalls caused by natural disasters at the historical lowest level, there will be no significant changes in the risk range of all counties/cities. Overall, natural disaster is a main source of food supply risk and population growth is the most common risk factor that could cause food insecurity in the Dongting Lake area; Resources and input elements will have a positive impact for future food supplies in most counties and cities. However, there will be no gap between supply and demand of food if we are considering Dongting Lake area as a whole.