The stool is thick and then thin, in addition to physiological factors, may also be caused by pathological factors, such as rectal cancer, colorectal fibroids, rectal polyps and so on. 1. Physiological factors: due to the different degree of water absorption of feces in the intestine. Because the feces formed by human body first will be stored in sigmoid colon, the longer it stays in colon, the more water will be absorbed to cause dryness and coarseness of feces, while the feces behind will be finer than the front end due to the shorter retention time and sufficient water in colon, as long as the number of defecation is normal, no blood in stool, no family history of tumor, age less than 45 years old and other high-risk factors, this is also belong to the normal Phenomenon. 2. Pathological factors: occupying lesions in the intestinal cavity, such as tumors or polyps, will make the stool thicker in front and thinner in the back. If the patient is accompanied by blood in stool and change of defecation habit, it may suggest rectal cancer. If the patient is accompanied by abdominal pain, abdominal distension and other discomforts, it may suggest colorectal fibroma, rectal polyps and other diseases.