Zhou-Yi was an originally divinatory book with some ideological thought. Yi-Zhuan was a book explaining how to reason auspicious and ominous results through the exploration of divinatory symbols styles. It deduced the laws of Yin and Yang in accordance with the forms of divinatory symbols. Moreover, it explained the law of life by going byond the limit of the divinatory symbols. So there were three thinking caps in Yi-Zhuan. In this way, the originally divinatory Zhou-Yi was transferred by Yi-Zhuan into a philosophy tome linking up the laws of universal life. The above-mentioned work of Yi-Zhuan is discussed in this article.