Zhu Xi's Yi-ology 易學is a complicated but unified theoretical system. "Yi was originally a book of divination" is the theory which can leading the whole ideology of Zhu Xi's Yi-ology system. By collated Zhu Xi's Yi-ology, correspondence, quotations and other related documents with the contents about the theory "Yi was originally a book of divination", and analyze the focus changes on this theory's thoughts before and after by chronological order. It could systematically interpret how did Zhu Zi's theory "Yi was originally a book of divination" affect the progress of Zhu Xi's Yi-ology and how to the respond to the gap between xiangshu 象數 and yili 義理,and also analyze the ins and outs of Zhu Zi's this theory is of great significance to study the history of Yi studies, the learning of Zhu Xi and the contemporary Yi studies.