To analyze regularity of compositions and medications for phlegm syndrome in Danxi's Mastery of Medicine and their internal relations.Methods:The prescriptions and formula treating phlegm syndrome in Danxi's Mastery of Medicine were collected，from which a database of formulas and medicines were established.The methods of data association rule algorithm and complex system entropy cluster were used to analyze the rules of prescription composition in Danxi's Mastery of Medicine for the treatment of phlegm syndrome with the software of TCM Inheritance Support System(Version 2.5).Results:Based on the analysis of totally 161 cases of prescriptions，the frequency of each herb included in the database was computed.The resulting new prescriptions contained “Indigo Naturalis，sea clam，Radix Glycyrrhizae，Fructus Trichosanthis” and “Rhizoma Arisaematis Cum Bile，Rhizoma Pinelliae，Semen Persicae，Poria”，etc.Conclusion:76% of the drugs for phlegm syndrome in Danxi's Mastery of Medicine belong to meridians of spleen and stomach.It prompts that in ZHU Danxi's academic thoughts of phlegm syndrome，regulating spleen and stomach is emphasized.The prescription is based on the principle of benefiting qi and reducing phlegm，and promoting blood circulation and removing blood stasis.On this basis，a new prescription for the treatment of phlegm syndrome is formed，which provides direction for the research and development of new drugs for phlegm syndrome.