Objective To establish the near-synonymous relationship between symptom terms in ancient Chinese medical books, and to provide terminological references for data mining, clinical research and intelligent diagnosis and treatment in Chinese medicine. Methods Based on the original data of ancient Chinese medical books, the symptom terms were manually annotated, standard words were sorted out according to industry standards and monographs such as Diagnostics of Traditional Chinese Medicine, Classification and Code of Basic Clinical symptoms of Traditional Chinese Medicine Information, and synonyms were classified and summarized to form the antonym database of ancient TCM books symptoms. 500 pairs of "standard -synonyms" words were randomly selected to form a questionnaire,and experts were invited to evaluate and analyze their content validity. Results 16, 456 pairs of "standard words synonyms" were formed by extracting symptom terms from 8 types of ancient Chinese medical books, including medical classics, typhoid fever classics, prescriptions, traditional Chinese medicines, Medical cases, diagnosis,comprehensive medical writings and acupuncture. The content validity index (I-CVI) was about 0.82. Conclusion The accuracy of the synonyms of TCM terms constructed in this study is high. The synonym database of ancient TCM books can promote the inheritance and research of clinical experience, and improve the accuracy and depth of data mining.