Flat stool with indentation may be caused by hemorrhoids, rectal polyps, intestinal tumors, anal stenosis and other diseases. 1. Hemorrhoids: when suffering from hemorrhoids, they can occupy the internal space of the intestinal tract and make it narrower and smaller. When the stool passes through the hemorrhoidal area, it can squeeze the stool, resulting in a change in the shape of the stool, which is flat, and there may be indentation. 2. Rectal polyps: are pathologic elevations that occur on the surface of the rectal mucosa of the organism. When there are polyps in the rectum, it can lead to narrowing of the intestinal tract, so that the stool is squeezed when it passes through the intestinal tract, and the symptom of flat stool occurs. 3. Intestinal tumor: when there is a tumor in the intestinal tract, the intestinal lumen will gradually become narrower with the increasing size of the tumor. When the stool passes through, it will produce obvious pressure on the stool, which will change the shape of the stool, resulting in the stool becoming flat, accompanied by indentation. 4. Anal stenosis: When there is congenital developmental abnormality in the anus and there is a history of surgery in the anus and intestines, it may lead to anal stenosis. In the process of defecation, the feces are compressed by the anus, which results in the appearance of flattened stools. When there is a flat stool with indentation, it is recommended to go to the hospital as soon as possible, to clarify the cause of the disease, under the guidance of the doctor to carry out targeted treatment.