The article (essay, thesis) aims at proving through analyzing the work that the theoretical background of Suseongji is largely based on the Doctrine of the Mean. In order to show that Suseongji is based on the point of view in line with the Doctrine of the Mean, we analyzed the work in that how the viewpoint of the Doctrine of the Mean is expressed in Suseongji, especially with the clue found in the excerpt. There was a work titled Uima created before Suseongji was born, in which the human mind was personified as a horse. The author must have had a desire to depict the human mind in a literature with a technique of personification. With such desire and trial, the work Suseongji has something to do with Uima by any regards. The work Suseongji has a threefold structure in which it accepts the viewpoint of the Doctrine of the Mean. The three parts of the work are not separated from each other, yet they keep changing to find a proper and desirable relations among the parts with regard to each other as the story develops. The point of view of the Doctrine of the Mean, which supports the changing process, works as an important guide. The characters in the work are also from the Doctrine of the Mean. They are not stable characters persisting one typical role or characteristic. The characters are not confined nor limited to a fixed framework, but they keep changing into different phases, which shows that the process is significant in the work. Thus, any single character is not valued over others. They are all important sharing their roles. The interpretation of the work in regard with the Doctrine of the Mean contributes to correcting the biased view on the work which has been approved so far. Diverse opinions are issued concerning the work. However, they are all extremes. The viewpoint suggested in this article has a significance in that it helps to find more diverse meanings in the past and also in the present from the work overcoming such problems.