Abstract: ZHANG Yuansu marked the medicinal properties of Yin and Yang in his book “Pearl Sac”, but the definition and connotation of the medicinal properties of Yin and Yang were not detailed and complete, and the understanding of the medicinal properties of Yin and Yang in academic circles for many years was still inconclusive. This paper uses the theory of traditional Chinese medicine and herbal literature as research materials, and uses the method of interpretation to study the medicinal properties of Yin and Yang in “Pearl Sac”. It is believed that ZHANG Yuansu's understanding of medicinal properties of Yin and Yang includes odor thickness lays the foundation of Yin-Yang property, odor consistently determines the “pure” of Yin-Yang property, universality and particularity elucidates the “micro” of Yin-Yang property, research and analysis integrates the differences of Yin-Yang property, and realistically decodes the secrets of Yin-Yang property. In the book “Pearl Sac”, the division of Yin and Yang properties of traditional Chinese medicine has the characteristics of multi-level, multi-angle and comprehensive. The interpretation of ZHANG Yuansu's medicinal properties of Yin and Yang can enrich the connotation of the theory of traditional Chinese medicine properties, which is conducive to clinical precision medication.

Key words: ZHANG Yuansu, “Pearl Sac”, medicinal properties of Yin and Yang, interpretation