”Chong-niu (重紐)” is one of the most complicated issues of medieval Chinese phonology. Mainly, there are two different views among the scholars engaged in phonological research. Some claim that phonetic differentiation exists in Chong-niu and that the differentiation has been studied from the aspects of vowels, consonants and medials; others believe that Chong-niu essentially reflects the differences of ancient pronunciation and that such differences had disappeared by the time when ”Qieyun” (a Chinese rhymed dictionary) was compiled. Scholars have racked their brains to study Chong-niu and have quoted extensively from the literature. However, there is a broad spectrum of opinions on this issue. Definitive conclusions have not yet been reached. This study aimed to elucidate Dr. Chen Bo-yuan's theory of Chong-niu. He believed that Chong-niu with different origins of ancient rimes had been considered to possess the same pronunciations as were extant in medieval China. Furthermore, the researcher will bring out insights and understandings based on Dr. Chen's study as well as the dissenting views of other scholars.