The dividing line between classical poetry and modern poetry is Shen Quanqi and Song Wenzhi in the early Tang Dynasty. On the basis of a lot of analysis and research on the rhythm and rhythm of poems before the Tang Dynasty, this paper puts forward that poems before the Tang Dynasty should be divided into two categories: ancient poems and modern poems. Modern poetry is relative to classical poetry and does not represent "modernity". Shen Quanqi and Song made great contributions to the formalization of modern poetry.