The theory of formulas corresponding to syndromes is one of the characteristics of Treatise on Cold Damage and Miscellaneous Diseases (Shanghan Zabing Lun) and one of the main principles in applying classic prescriptions. It is important to take effect by following the principle of formulas corresponding to syndromes. However, some medical practitioners always feel that the actual clinical effect is far less than expected. Six errors in the use of classic prescriptions as well as the theory of formulas corresponding to syndromes are the most important causes to be considered, i.e. paying attention only to the local syndromes while neglecting the whole, paying attention only to formulas corresponding to syndromes while neglecting the pathogenesis, paying attention only to syndromes while neglecting the pulse diagnosis, paying attention only to unilateral prescription but neglecting the combined prescriptions, paying attention only to classic prescriptions while neglecting the modern formulas, and paying attention only to the formulas but neglecting the drug dosage. Therefore, not only the patients' clinical syndromes, but also the combination of main syndrome and pathogenesis simultaneously is necessary in the clinical applications of classic prescriptions and the theory of prescription corresponding to syndrome. In addition, comprehensive syndrome differentiation, modern formulas, current prescriptions, combined prescriptions, and drug dosage all contribute to avoid clinical errors and improve clinical effects.