Objectives : In this article, an analysis of some documents about medical thought of change in medical history explains how the concept of it has been established and expanded, and through that, we can find the fusion of tradition between medicine and the study of IChing. Methods : Through investigation and analyses of the texts about medical thought of change in important medical books, the contexts of the history will be drawn. Results : Although the study of IChing and medicine have been developed separately in the early period of medical history, it has been started to fuse explanations for symptoms and mechanisms of diseases using trigram images. Yin-yang and wuxing changes(陰陽五行) of human body have been explained with 12 changing trigram(消息卦) and eight trigram(八卦). In the Ming dynasty, the establishment of Myeongmun(命門) theory was influenced largely from IChing, but it was followed by a scathing criticism of some doctors in the Qing dynasty. Conclusions : Developing of the study about Iching and medicine, thought of change has been an important foundation of new theories in traditional medicine like as the issue of Myeongmun theory, as a result, it has contributed to the development of clinical medicine.