Determining treatment principles according to syndromes， then selecting formula according to the principles， or deciding on herbal medicines to compose a formula consist in syndrome differentiation of Chinese medicine. Correspondence between “syndrome and formula factors” reflects the corresponding relationship between dominant medicine (formula-factors) and the pathogenesis (syndrome-factors). By analyzing the corresponding relationship between formula-factors and syndrome-factors of representative formula of six meridians from Treatise on Febrile Disease， and understanding compatibility of classical formulas is conducive to guiding selection and composition of classical formula in clinical practice.