Abstract: The origin, development, and maturation status of the spleen-yin theory in the history of Chinese medicine are discussed. The main contents of the spleen-yin theory are introduced, including its vital role in the process of spleen transport and transformation, the syndrome characteristics of spleen-yin deficiency and the key to identify it, as well as the treatment of spleen-yin deficiency by nourishing and benefiting yin with sweet-cold medicines. After Miao Xi-yong, the spleen-yin theory was further developed. The modern theoretical research on spleen-yin theory mainly includes three aspects: the study of the connotation of spleen-yin, the study of the differentiation points between spleen-yin deficiency and stomach-yin deficiency, and the study of the treatment of spleen-yin deficiency. The modern clinical application of spleen-yin theory is mainly applied to various gastrointestinal diseases.