It is well known that the relationship between “m-tail” and “n-tail” has always been the focus and difficulty of linguistic research. In the medieval phonological system, the rhyme of “Shen、xian” Ershe has a“m-tail”, while in the modern phonological system, except in some dialects of Guangdong, Fujian, Eastern Zhejiang and Jiangxi, the-m-tail is not found in other dialects. Mandarin has no - M tail. Through the rhyme analysis of Quanming Sanqu, the author finds that the transformation of - M end not only appears in southern Sanqu works, but also in northern Sanqu works. Therefore, taking “m-tail” and “n-tail” in Quanming Sanqu as the research object, this study will discuss the mixed leaves of “m-tail”, “m-tail” into “n-tail” and “n-tail”. Through comparative analysis, we can draw the conclusion that although there are some phenomena of “m-tail” being used alone in the works, the opposition between “m-tail” and “n-tail” in the Ming Dynasty has disappeared, and the “m-tail” has gradually shrunk and turned to “n-tail”.