Abstract: The logic of food security from the national perspective is "politics taking precedence over economy". The former determines the national strategic positioning of food security and the latter determines the national policy ideas about ensuring food security. The particularity of China's food security problem is that the main role of the state has been greatly strengthened. Food security is regarded as a major strategic issue and an important basis for national security. In order to implement this positioning, the national policy idea for a long time is to improve the self-sufficiency rate of important agricultural products through strong market intervention. The strategic transformation of China's food security is from passive strategy to active strategy, from relying on small-scale farmers to relying on large-scale management. The premise of realizing this transformation is to promote the comparative advantage of the grain economy through the transformation of agricultural production organization so as to improve its international competitiveness. The policy design of food security in the transition period should adhere to the methodology of bottom-line thinking and correctly understand the relationship between grain security and big food security.