This paper is intended to compare Zhu Xi's and Cheng Yi-chuan's Yi theories in terms of how Zhu succeeds, refashions, or recreates Cheng's theory; it is also explained why Zhu and Cheng are different. We show firstly how they value Confucianism and Yi Jing and compare their different approaches to and annotations ofYi Jing as well as the developments of their respective studies ofYi Jing. The things Zhu inherits from Cheng are mainly: Cheng's annotation ofYi Jing in terms of meaning, the Confucian approach to Yi Jing with its emphasis on human lives, the everlasting dynamic ontology, the coordination of Ying and Yang, and the interpretation of the ontological hierarchy in terms of Dao and Qi. Besides, there are six differences between them as well: first, Cheng disregards augury and the theory of Feng-shuei as a kind of pseudo-science, while Zhu respects and explains these theories; second, Cheng values the middleway while Zhu appreciates the transformation of Ying and Yang; third, Cheng emphasizes on particularity and specificity while Zhu prizes universality; fourth, Zhu is superior to Cheng in the field of exegetics; fifth, Zhu's theory of Yi is more encompassing, while Cheng treasures only Xu Gua Zhuan; sixth, Zhu highly appreciates Zhou Lian Xi's Tai Ji Tu Shuo, especially the idea ofTai Ji, while Cheng doesn't even mentions it.