Balance of yin and yang, health preservation and disease elimination: the secret of yin and yang is a high summary of the best life activity state of human body in Huangdi Neijing. The secret of yin and yang, that is, the overall harmonious state achieved by the interaction of yin and yang while maintaining their respective functions and characteristics, is an abstract summary of the complex relationship and organic connection between various functions in life activities. In normal people, the physiological state of "Yin-Yang Pingyang Secret" can be summarized as the following aspects: the channels and collaterals are unobstructed, the nine-waiting and four-pulse, the cold and warm coexist, the shape and flesh are matched, the qi and blood are harmonized, and the viscera are coordinated. If yin and yang are unbalanced, the above physiological processes will inevitably be abnormal. Once the relationship between Yin and Yang is lost, the "secret of Yin and Yang" will collapse and life will end.