In the past, historians tended to interpret the Confucian intellectuals' engagements with Daoism as an attempt to stay isolated from the secular world, and considered it a response to the dynastic change from the Song to the Yuan period. From the perspective of intellectual history, this essay attempts to provide an alternative interpretation. To begin with, Zhu Xi's theory of Yi Xue (study ofthe Book of Change) will be elaborated. Specifically, this essay argues that the way he interpreted Yi-Tu and Xiang-Shu broke the boundary between Confucianism and Daoism. Taking the study of the ZhouyiCantongqi for example, in their studies of Yi Xue Zhu Xi and his fellows obviously took note of the Xiang-Shu theory from the Cantongqi. Moreover, they were also involved in the practice of alchemy when studying the Cantongqi. After the mid Southern Song, more and more intellectuals followed in Zhu Xi's footsteps and sought the principles of the universe usingYi-Tu and Xiang-Shu, instead of relying on the Zhou Yi alone. This approach further motivated other intellectuals to investigate the theory of Xiang-Shu in other Daoist classics and the alchemical traditions. They did so with the purpose of enhancing the explanatory power of Yi Xue in terms of the principles of the universe. Eventually, functioning as a medium, Yi-Tu and Xiang-Shu helped create a common worldviewas well as the concepts and vocabulary shared by Daoists and Neo-Confucians. This provided an intellectual foundationin the Song-Yuan period, for the Confucianintellectuals engaging with Daoism and sometimes even becoming Daoists themselves.