The theory-the doctrine of Confucius and Mencius was an objective existance in Chinese dietary culture history, but it was ignored in the last two thousand years. In addition, some people misunderstood Confucius' and Mencius' thoughts and statements. This paper believes that the doctrine of Confucius and Mencius is Confucius' and Mencius' diet opinions, thoughts, theories and basic style in their diet experiences. Confucius' diet experience and Mencius' diet experience were alike, and Mencius' experience carried on Confuius' and theirs were the same in some sections. They all stay their diet standard to their stomach and don't persue good meal. They all thought resolving people's diet was important for a country and for the politic problems. Mencius succeeded Confucius' diet thoughts and put them to the theories-diet principle, diet standard, and diet morality. This paper deeply discusses theory, developing history condition and the affection and position in Chinese diet history of the doctrine of Confucius and Mencius.