Following the Book of Songs, in the 4th century BC, a new style of poetry appeared in the State of Chu, called Songs of the Chu, and its founder was Qu Yuan. Later, the Han people compiled the works written by Qu Yuan, Song Yu and others into a book called Songs of the South. The Songs of Chu broke through four sentences in the Book of Songs and developed into five-character sentences and seven-character sentences, that is, even sentences (four words in a sentence) were changed into odd sentences (five words in a sentence and seven words in a sentence), which not only better expressed thoughts and feelings, but also made the rhythm and rhythm more musical.
In the Han Dynasty, Yuefu Poetry, a poem sung with music, appeared. There are four words, five words and miscellaneous words in language, but most of them are five words. Later, the literati headed by Cao Cao and his son and Tao Yuanming developed five-character poems. At the same time, seven-character poems have also developed greatly.
Before Wei, Jin, Southern and Northern Dynasties, the rhythm and rhyme of poetry had not formed a rule that everyone followed, but the author wrote it according to his personal content needs and rhyme feeling. In the Wei and Jin Dynasties, influenced by Indian Sanskrit phonology (called Tianzhu in ancient times), phonology in China developed. Zhou Ai and Shen Yue of Qi Liang summed up the pronunciation rules of Chinese characters and put forward the theories of "four tones" and "eight diseases", which made poetry creation develop from natural rhythm to pursuit of rhythm, and the nature of paying attention to levelness and rhythm appeared in poetry writing, forming the main content of metrical poetry.