Fang Yuan is defined as the smallest unit of prescription composition in Treatise on Febrile Diseases，which not only reflects the characteristics of prescription formulation but also facilitates flexible application in clinical practice.This study aims to analyze the medication rules in Treatise on Febrile Diseases from the perspective of Fang Yuan using data mining methods.Methods:In this study，R language was employed to calculate the Jaccard similarity coefficient between different prescriptions and the association rules among various Chinese medicinal herbs.Network community structure analysis was utilized to identify Fang Yuan in Treatise on Febrile Diseases.Results:The similarity among all prescriptions in Treatise on Febrile Diseases was significantly higher than that of prescriptions in the textbook of Fang Ji Xue，indicating the existence of smaller prescription units.Association rules and community analysis were able to identify Fang Yuan，such as Fang Yuan composed of two medicinal herbs including gypsum-licorice，cassia twig-angelica sinensis，gardenia-fermented soybeans，as well as Fang Yuan composed of three medicinal herbs such as dried ginger-coptis-ginseng，angelica sinensis-asarum-woody nightshade，and ephedra-cassia twig-apricot seed.Conclusion:Treatise on Febrile Diseases contains Fang Yuan composed of two or three medicinal herbs.Future research should validate these Fang Yuan clinically or experimentally to clarify their therapeutic effects and guide their application in clinical practice.