This paper expounds the theory of health preservation, and further explains the principle of "Yin and Yang as the method, harmony with surgery, moderate diet, regular daily life and no rash action" pointed out in ancient naivety. Based on the clinical etiology and the principle of yin and yang of human body, this paper points out the important functions and specific precautions of adapting to the five elements, transporting and transforming six qi, quiet environment, working day and night and eating five flavors.