Constipation after the anus is getting smaller and smaller may be caused by anal and intestinal diseases, such as anal fissure, hemorrhoids, tumors and so on. 1. Anal fissure: it is a small ulcer formed by splitting the skin of the anal canal in its entirety, and its clinical manifestations are pain, blood in the stool and constipation. Constipation due to dry and hard stools, defecation will lead to anal fissure ulcer cracking, and then gradually healed. This repeated process leads to the formation of scarring of the skin at the site of the anal ulcer, thus causing anal stenosis. 2. hemorrhoids: constipated patients due to increased abdominal pressure and dry stools are more likely to induce hemorrhoids, hemorrhoids prolapse more will indirectly lead to anal stenosis, such as the third stage of mixed hemorrhoids, the anus will have prolapsed mass, and can not be returned to the anus by hand. 3. Tumor: for example, low rectal cancer, anal cancer and so on, due to the invasion of cancer can also lead to anal stenosis. If constipation occurs with anal stenosis, it is recommended that the patient should go to the anorectal department of the hospital in time to clarify the cause of the disease and give targeted treatment.