“知_知”、“支_章”两字在《广韵》都是止摄开口三等支韵字,在《中原音韵》分属齐微韵和支思韵,它们的分化可以由韵母演变造成,擦音与塞音、塞擦音不同步发展是其中一个重要原因:庄组字首先变读支思韵,章组字具备变读擦音的成员而知组字没有,致使章组先于知组与庄组字合流变读支思韵。这样《中原音韵》“知”、“支”分韵可以由知庄章三组声母字合一情况下韵母的对立造成。 “Know _knowledge”, “支 _ 章” in the word “Guangyun” are the third photo of the opening and closing words, in the “Central Plains rhyme” belong to Qi Yun and support Si Yun, their Differentiation can be caused by the evolution of vowels. One of the important reasons is that rubbing and stoppening are not synchronized with each other. Cause chapter group prior to Zhizhu and Zhuang group word combination read support Si Yun. Such “Central Plains rhyme” “know ”, “branch ” sub-rhyme can be caused by the opposition of the consonants in the case of three consonants of Zhuangzhang.