ABSTRACT
“Three Yin and Three Yang” syndrome differentiation is a method and system generated from “Treatise on Febrile Diseases”. And it is a principle of syndrome differentiation and a criterion of treatment. Modern physicians give many descriptions on levels of “Three Yin and Three Yang” syndrome differentiation. There are a lot of different opinions on it, including “Yin and Yang”, ”three steps of Cluster analysis”, “one divided into two” combining with “one divided into three”, and “three steps of recognizing symptom, understanding disease and differentiating syndrome” theories. The author believes “Three Yin and Three Yang”syndrome differentiation consists of three levels:differentiating syndrome principle, differentiating syndrome category and differentiating syndrome type. Strengthening research on levels of syndrome differentiation helps to improve accuracy of syndrome differentiation, guide drug description and enhance clinical efficacy.