Abstract: In order to discover the reasons for food shortages in Southern China, this paper analyses grain supply and demand in the Southwest karst shrub land and Southeast forest-shrubland regions. From 2000 to 2009, Southern China’s grain output remained stable at approximately 220 million tons. Grain ration consumption, on the other hand, declined from 138.50 million tons in 2000 to 106.77 million tons in 2009. This result shows that food shortage is not caused by ration consumption. In 2009, Southern China’s forage grain amounted to 79.9 million tons, accounting for 33.9% of total grain yield. In the same year, industry grain amounted to 62.3 million tons and 26.8% of total production. Grain ration, forage grain and industry grain constitute the three parts of total grain demand in Southern China, while non-food grain accounts for about 57.3% of the total demand for grain and is the main factor affecting food security. The difference between grain supply and demand in 2009 was some 14.2 million tons, which means that at least this amount required transportation from north to south, a situation that involves substantial costs, as well as effectively wasting about 2.8 million m³ of water resources. If successfully applied to Southern China’s grassland agriculture, the concept of “large grain, large resource, intensive agriculture” could make better use of ecological resources, protect the consumption of forage grain and supplementary grain rations, reduce grain demand and increase grain supply at the same time. Furthermore, the sunlight intensity of Southern China is low, giving its grasslands many comparative advantages. The paper thus concludes that developing suitable grassland agriculture models is a reasonable way to solve the problem of food shortages in Southern China.