Diarrhea is a common clinical illness which is discussed in detail in the Treatise on Exogenous Febrile Diseases. Eighty pieces of article mentioning diarrhea are cited in the book, indicating that diarrhea can be treated according to various meridians such as Taiyang Meridian, Yangming Meridian, Shaoyang Meridian, Taiyin Meridian, Shaoyin Meridian, and Jueyin Meridian. This study briefly analyses diarrhea from the perspective of Six Meridians in Treatise on Exogenous Febrile Diseases. By distinguishing and analyzing the Law of Diarrhea, this thesis is valuable for making the full use of the classical prescription and improving clinical treatment of diarrhea.