Although Guo Yu is a historical book, its emphasis is on argumentation, many of which involve aesthetic issues, among which the most important ones are about the concept of “Mei”. These concepts are: Firstly, “Wen”(text, literary composition). “Wen” has many meanings, one of which is Mei. Secondly, “Zhang” (chapter, section, rule). “Zhang” has many meanings, almost summarizing the basic nature and characteristics of Mei. Thirdly, “He” (harmony, mix, peace). Music pays special attention to “He”. In fact, it is not only music that emphasizes “He”, but all beautiful things value “He”, since it is the essence of Mei. The composition of “He” is a combination of many factors. The realization of “He” is the creation of new things. Fourthly, “Mei”. Guo Yu defines “Mei”. From this definition, we can derive the basic properties of “Mei”: harmless, beneficial, virtuous, courteous and respectable. At last, “Mao” (appearance, looks). Guo Yu believes that “Mao” is important, but words are more important than it. Words are the voice of the heart, and the heart determines words. The “Mei” theory in Guo Yu is almost a collection of the pre-Qin Confucian “Mei” theory.