Objective: The aim of this study was to analyze the medication rule in herbal prescriptions for knee osteoarthritis by using Chinese medicine inheritance support system (TCMISS). Method: The herbal prescriptions for knee osteoarthritis from papers were collected

then the data were input into TCMISS and composition principles were analyzed by using data mining methods such as revised mutual information

complex system entropy cluster and unsupervised hierarchical cluster. Result: Based on the analysis of 263 herbal prescriptions

the frequency and meridian entry distributions of each herb were found

association rules among the herbs were computed

16 core combinations and 4 new prescriptions were mined from the database. Conclusion: The common Chinese medicines used for knee osteoarthritis included blood-activating and stasis-resolving medicine

blood-tonifying medicine

qi-tonifying medicine

wind-dampness-dispelling and cold-dispersing medicine. The major components of the Chinese medicines for knee osteoarthritis were the medicines which have the function of tonifying the kidney or activating blood. The meridian entry distributions of herbs are composed of liver meridian and kidney meridian. The method of treatment for knee osteoarthritis are to regulate the liver and supplement the kidney

activate blood and resolve stasis.TCMISS contribute to the study of composition principle lawof herbal prescriptions.