Abstract: About the problem of opening-closing mouth of labial words in Qie Yun, there are two different opinions in academia. One school claims that we should not differentiate opening from closing mouth of labial words in Qie Yun while the other stands on a different ground. Through sorting out the research status of the problem of opening-closing mouth of labial words in Qie Yun, this thesis questions the articles of Mr. Huang Yiqing, Mr. Ruan Tingxian and Mr. Chu Taisong. As we don't have sufficient evidence, we should keep a conservative attitude to the problem of opening-closing mouth of labial words in Qie Yun. And we'd better not differentiate opening from closing mouth of labial words in Qie Yun.