Zhou Deqing's (1277-1365) ”Zhongyuan yin yun” annotates that his book serves as ”a model for 'zhengyu' and a rectification of 'bianya'.” Based on this statement, this article will explore his Rules for Composing the Traditional Northern Opera with Correct Sounds in the book. In addition, according to Zhou's understanding of ”entering tones are situated between breathing and speaking,” the author will investigate Zhou's construction of ”zhengyu” theory. This article is divided into four sections. After an introduction in section one, section two explicates the linguistic background and meaning of the above mentioned statement. This statement signifies that the pronunciation in Zhou's book was deemed standard in the Central Plains, rectifying the disadvantages of various dialects, and differentiating divergences among ”Guang yun” and various types of operas in Chinese dialects. Section three compares the following rhyming phenomena: level tones divided into voiceless and voiced level tones, entering tones recategorized into level, rising, and departing tones, and a lack of closed entering tones and rhyming. Section four analyzes the subject dialects that Zhou rectified, especially the Wu dialect in Song-Yuan southern drama. Grounded in the differences between ”Zhongyuan yin yun” and ”Guang yun”, Zhou fulfilled the objective of ”a model for 'zhengyu'” and brought the aim of ”a rectification of 'bianya'” to a successful conclusion through the comparison of central pronunciation with the Wu and other dialects. Not completely agreeing with what ”Guang yun” argues, he viewed dialects as having deficiencies and meanwhile accepted them as pronunciation in common practices. His goal of composing ”Zhongyuan yin yun” was to historicize the changes of sounds and therefore normalize pronunciation for traditional Chinese opera.