Objective: To explore the compatibility and application methods of clinical formulas.Methods: In the guidance of monarch,minister,assistant and guide theory, the constructions of prescription were divided into principal agents and lesser agents;500 prescriptions were from 1000 set prescriptions and empirical formulas recorded in pharmacology of traditional Chinese medical formulae teaching material and well-chosen efficacy nostrum written by national lever famous veteran teran doctors of TCM.Then they were analyzed to study the constituting formats of(clinical) formulas and the derivation methods of set prescriptions in clinical application.Results: Through analysis,we found the constituting formats of formulas in terms of single taste single group having principal agents but lesser agents(12.3%),multitude groups having principal agents but lesser agents(13.7%),single taste or single group principal agents with one group lesser agents(14.4%),multitude groups principal agents with one group lesser agents(17.7%),single taste or single group principal agents with multitude groups lesser agents(18.3%) and multitude groups principal agents with multitude groups lesser agents(23.6%) et al.From the 500 randomly extracted prescriptions,among 68.4% prescriptions were present derivation relationship,that is,for adapting new pathogenesis conditions,through methods in terms of replacing principal agents(10.2%),mild recipe lowering to lesser agents(17.0%),two formulas to put together(14.3%),expanding principal agents(16.4%),changing lesser agents(18.7%),principal agents pero-replacing(10.2%) and others(13.2%),changed constituted relation of principal agents or lesser agents,so to generate several formulas possessing new effect characteristics.Conclusion: The(divide) of principal agents and lesser agents has a universal applicability in analyzing the constitutions of formulas;the clinical application and derivation methods of set prescriptions revealed by this method have guide effect to initial(experiencing) clinical worker.