Zhouyi evolved the thought of “sincerity” into a metaphysical realm level. The discussion of “ sincerity” in the pre-Qin period mostly focused on “practice”, and Zhou Dunyi promoted “ sincerity” to the Tao to realize the communication between heaven and humanity. Moreover, Zhou Dunyi highly praised the Confucian classic Zhouyi, and his thought of “sincerity” mostly came from his elucidation and expansion on Zhouyi. He gave “sincerity” a new meaning on the basis of the interpretation of the meaning of Zhouyi. The regulation of “ sincerity” in Zhouyi comes from the elucidation of the divination and argumentation of Zhouyi. The two cultivation methods of “sincerity” are also in view of the internal cultivation methods advocated in Zhouyi. Zhou Dunyi inherited the metaphysical realm form of Zhouyi to make “sincerity” reach the destiny of heaven and establish the pole of man. It can be seen that Zhouyi plays a very necessary role in the construction of Zhou Dunyi’s ideological system of “sincerity”.