The purpose of this study is to find out how popular pronunciations of Chinese characters have occurred. For this, I choose some Middle Chinese texts like Longkanshoujing 龍龕手鏡, Xinji Zangjing Yinyi Suihanlu 新集藏經音義隨函錄 etc. for main text which are dictionaries for Chinese Characters specializing in Buddhist texts in Middle Chinese period. These contain copious notes about the popular pronunciations of Chinese characters in Middle Chinese. From these texts, I established the cause of the popular pronunciations. The popular pronunciations are caused by these reasons.: misread, reading as variant forms, taboo and dialects. Most cases are misread and reading as variant forms, and occur almost unconsciously.