Objective To explore the drug compatibility and relevant medication rules in applications of Realgar in the treatment of sores and poison in ancient doctors.Methods Realgar prescriptions recorded in classic ancient books of Chinese ancient doctors were searched based on the "General Catalogue of Ancient Books on Chinese Medicine",so as to establish a relevant prescription database,and then,a statistical analysis on the frequency of drug use,four characters,five tastes,nature,flavor and channel tropism was conducted based on the database.Subsequently,the drug association rules and visual network diagrams were analyzed,so as to demonstrate the connections between drugs comprehensively.Finally,a cluster analysis was conducted to explore the classification of drugs for clinical use.Results A total of 459 prescriptions containing Realgar were included in the study,involving 480 kinds of drugs,and the accumulative times of medication reached 2980.There were 32 drugs with accumulative frequency ≥80%.In the prescriptions concerning Realgar,Cinnabar,Musk, Radix Aconite Lateralis Preparata,Alum,Croton and Bezoar were used for more than 60 times as high frequency drugs.For the nature and flavor,both warm and cold drugs were used,with pungent and sweet(light)flavors as the main.For channel tropism,liver,spleen,and heart meridians were dominant.The analysis on the drug association rules and visual network diagrams showed that the drug combination with the highest support was Realgar-Cinnabar,followed by Realgar-Musk.The cluster analysis results showed that high frequency drugs could be grouped into 5 categories.Conclusion A systematic analysis on the Realgar medication rules of ancient doctors for treating ulcer and carbuncle may be performed based on a data mining method,so as provide references for safe application of Realgar in modern clinical practice.