Abstract: This article explores the compatibility of traditional Chinese medicine for external treatment of ulcers from the perspective of "the principle of internal and external treatment" in Rhymed Discourse on External Remedies. First, it discusses the clinical understanding of chronic skin ulcers, and then it explains the connotation of "the principle of internal and external treatment", which has the characteristics of theoretical homology, syndrome differentiation and treatment, and focusing on the property and taste of the medicine first. Finally, based on "the principle of internal and external treatment", it discusses the compatibility ideas of Chinese medicine for external treatment of ulcers, and specifically analyzes the compatibility ideas of property and taste and monarch, minister, assistant and envoy, so as to provide some reference for the external treatment and compatibility of Chinese medicine for chronic skin ulcers, and also hopes to provide some directions for the research and development of external traditional Chinese patent medicines and simple preparations.