“The treatment of both large intestine and small intestine”comes from a book called Systematized Identification of Warm Disease(Wu Tang ). Defecation and urination are the portals of the internal environment of the body. And The large intestine and small intestine are the sites where urine and feces are produced and discharged. Clinically, there are many common diseases about urine and feces, And about large intestine and small intestine. In the past, doctors paid more attention to the relationship between the large intestine and other viscera, Or the relationship between the small intestine and other viscera. But few people think about the relationship between the large intestine and the small intestine. Based on the liquid and fluid theory , this paper analyzes the internal connection of the large intestine and small intestine from three perspectives of Physiology, formula and classic case,and How do we use it in clinical.