Abstract： The effective prescriptions contained in Shanghan Zabing Lun have been repeatedly verified in clinic. The flexible application of classical prescriptions should be based on accurately grasping the pathogenesis，and the prescriptions cannot remain unchanged. The application of Didang tang is based on the pathogenesis of binding of stasis and heat；Banxia Houpo tang on qi stagnation and phlegm coagulation. Guizhi and Longgu Muli tang can be used flexibly according to syndrome differentiation for those with yin- yang disharmony and disharmony between ying and wei qi. Therefore， Didang tang for antiphospholipid syndrome， Banxia Houpo tang for sjogren syndrome and Guizhi and Longgu Muli tang for postpartum rheumatism are classic prescriptions which verify the principle of "observing and distinguishing the pathogenesis and treating the disease". The application of classic prescriptions nowadays is flexibly performed，by using the prescriptions，or learning the methods，or taking the meaning. By distinguishing pathogenesis for treatment and properly modifying the prescriptions， regardless of the disease names in ancient or modern times， the innovation of new applications can improve the curative effect of complex or refractory diseases.