Food security is similar to food safety from literal meaning, but their focuses are dissimilar. The paper discusses their key topics and logic relationship from the perspective of social economic evolution. The issue of food security stems from the situation of food shortage, but rationality of food safety is that there are more and more hazard factors in food. They are both difficult problems that the society has to face during the different development periods. Today, market economy system, agricultural technology, and industrial policy have mitigated the situation of food shortage dramatically, however, the measures of pursuing more output and lower cost may bring negative effect on food quality.