Treatise on febrile diseases also has an important creation in syndrome differentiation and treatment, that is, when diagnosing diseases, it focuses on yin, yang, exterior and interior, cold and heat, and excess and deficiency, which are collectively called "eight classes", with yin and yang as the general program. Exterior, heat and excess yang; Cold inside, deficiency belongs to yin. For strong people, exogenous diseases turn from yang to exterior, heat and excess. For people who are weak, diseases and pathogens mostly turn from yin to become internal, cold and deficiency syndromes. The diagnostic method of syndrome differentiation of the eight cardinal principles is to apply "four diagnoses", that is, looking, smelling, asking and feeling. By observing the patient's complexion, body shape, tongue quality, listening to the patient's voice, smelling the patient's excrement, asking about the medical history and existing illness, and understanding all aspects of the illness through pulse diagnosis and skin diagnosis, we can get the impression of the depth (exterior and interior), cold and heat, ups and downs (excess and deficiency) of the disease, and then get the conclusion that the disease belongs to a certain type of Sanyang and Yin San respectively. Zhang Zhongjing's Treatise on Febrile Diseases attaches great importance to the changes and illusions of diseases. For example, some syndromes are similar to excess heat syndrome, but the pulse is weak, or the limbs are syncope, but the pulse is steady and powerful, which are all phenomena of "true winter vacation fever" or "true heat and false cold". Treatise on Febrile Diseases has many rules. In addition, Zhang Zhongjing also believes that in the diagnosis of diseases, pulse conditions and syndromes should be referred to each other to obtain the basis of diseases, and sometimes it is necessary to "follow the syndrome instead of the pulse"; Sometimes, it is necessary to "give up the root and get rid of the end", said in Volume II of Li Zhongzi's "Doctors Must Read" in the Ming Dynasty. "Zhong Jing said: fever, headache, heavy pulse and body pain should be preserved. Using Sini decoction is self-sinking pulse." He also said: "Shaoyin disease has a fever at the beginning, but the pulse is heavy. Mahuang Fuzi Asarum Decoction is slightly sweaty, ... from the syndrome but not from the pulse."