There are many reasons for anal distension and poor ventilation, such as constipation, indigestion, hemorrhoids, intestinal obstruction and so on. 1. Constipation: daily improper diet, not to develop good defecation habits and other factors caused by dry stool, constipation, due to the accumulation of feces in the intestinal tract, can lead to anal distension, ventilation is not smooth. 2. Indigestion: Eating too much indigestible food, resulting in indigestion, can also cause food residue, feces accumulation in the gastrointestinal tract, thus causing anal distension, ventilation is not smooth, accompanied by abdominal distension, abdominal pain and other symptoms. 3. Hemorrhoids: hemorrhoids, if more serious, can also lead to anal distension, ventilation, mainly due to hemorrhoids on the mucosal blood vessels tortuous, expansion and other factors, or with edema, infection, hemorrhoidal nucleus swelling caused by the phenomenon of defecation will also occur. 4. intestinal obstruction: intestinal obstruction due to a variety of reasons so that feces blocked in part of the intestinal lumen, can not be normal peristalsis, there will also be anal distension, ventilation, at the same time can be accompanied by abdominal pain, abdominal distension, the individual to stop defecation, defecation and other phenomena. There are many reasons for anal distension, ventilation, not smooth, after the emergence of symptoms, it is recommended to go to the hospital in a timely manner, do not ignore the symptoms, so as not to delay the treatment of the condition.