Abstract: Yi Zhuan puts forward the value principle of “keeping harmony” from the cosmological point of view,and combines with the theory of position to implement it as a kind of practical wisdom of accumulating potential,abstaining from hyperactivity and being positive for good.The concepts of “middle” and “middle use” in Yi Zhuan are mainly embodied in the biography of Yuci Zhuan in 64 hexagrams and the biography of Xiangci Zhuan in two and five hexagrams.In the structure of hexagram formed by the six trigrams,the first and the fourth ones are in the lower position of the upper and the lower ones,which is similar to “inferior”;the third and the upper ones are in the upper position of the upper and the lower ones,which are similar to “over”,which are not perfect;the second and the fifth ones are in the “middle” position of the lower and the upper ones respectively,which symbolize “middle” in dealing with affairs,which is more auspicious than other ones.Heaven diagram in Zhouyi,Yuci Zhuan,Xiangci Zhuan and Wenyan Zhuan embody the practical value orientation of “keeping harmony and being good”.