This paper analyzed the food production by the households in the counties with high population (Mizhi County) and low population (Wuqi County) in North Shaanxi, and studied the food security and its affecting factors in the two counties by using minimum cropland area per capita and Cobb-Douglass production function methods. The results demonstrated that the food production in low population county could meet the basic standard of food security, while that in high population county could not. Cultivated area and investment in agricultural technology were the major factors affecting food security; labor force, labor quality, and grain subsidy also had positive effects on food production. The current technology and labor quality did not reach their potential for food production. This region needed to increase grain production area to reach the minimum standard of 0.14 bm2 per capita, put much stress on labor force training, and formulate appropriate following policies for 'Grain for Green' to realize the food security strategy.