Anal pain when diarrhea is common in the following cases: 1, anal fissure: anal fissure is one of the more common causes of anal pain during defecation, because if itself has anal fissure, it is manifested as a fissure tear caused by the contraction of the sphincter muscle when the stool passes through the anus, triggering pain, if the number of diarrhea, repeated stimulation of the anal muscles, pain will continue to increase, the fissure will become deeper and the pain longer. 2, hemorrhoids. Patients themselves have hemorrhoids exist, diarrhea defecation, long squatting and sitting on the anal local pressure increases, venous reflux is obstructed, leading to the formation of thrombosed external hemorrhoids, inflammatory edema, defecation through the pressure on the nucleus, will lead to severe pain, it is recommended to use drugs to treat diarrhea, and then use hemorrhoid cream on the nucleus for local application, with anti-inflammatory, swelling, pain relief, or Chinese herbal fumigation, if necessary, surgical removal.