In early stage, it is confined to mucous membrane, and there are no obvious symptoms, sometimes there is a small amount of bleeding, which is difficult to be detected by naked eyes, but when the cancer grows and has ulcer and infection, the following symptoms may appear. Abnormal bowel movement, i.e. rectal irritation symptoms, such as frequent bowel movement, falling, incomplete bowel movement, or even urgency and heaviness, as well as abdominal distension and lower abdominal discomfort. The change of these habits is mainly caused by the stimulation of rectum by tumor lesions or cancerous foci combined with infection. The main manifestation is the increase in the number of stools, from several times a day to ten times a day, or even dozens of times a day. At the same time, there is a continuous feeling of anal swelling and the feeling of incomplete defecation. 2, stool abnormalities, there is obvious bleeding at the time of defecation, the amount is small, and there is mucus discharge at the same time. In case of serious infection, there is pus and blood stool and the number of stools increases. Blood in stool is the most common symptom of rectal cancer patients. The cause of blood in stool of rectal cancer patients is the same as other parts of colon cancer, which is due to the oozing of blood after the surface of the cancer breaks down to form erosion and ulcerated surface, except that it is more likely to occur, the surface of the cancer is more likely to be rubbed by solid stool, and blood is less likely to be mixed with stool than upper colon cancer. Blood in stool is mostly fresh blood or dark red blood, which is not mixed with stool. Large amount of bleeding is rare. Sometimes the blood in stool contains blood clots and detached necrotic tissue. In fact, patients with rectal cancer can have the symptom of blood in stool in early stage, which is often misdiagnosed as “hemorrhoid” in clinical practice. Therefore, patients with blood in stool should be examined by rectal examination. Moreover, because the ulcerated surface of the tumor is easily combined with infection, patients may have pus or mucus in the stool, which, together with the original symptoms of blood in the stool, may be easily misdiagnosed as “chronic bacillary dysentery” and treated. 3.Obstruction symptoms The rectum is obstructed by the cancer, with difficulty in defecation, less stool and closed stool, or even thin stool shape. Deformed and thin stool accounts for 39.5% of rectal cancer patients. In case of severe intestinal stenosis, feces will be difficult to be excreted and will be collected in the rectum, and water will be further absorbed, resulting in dry stool and further difficulty in defecation and constipation. Rectal cancer has the manifestation of intestinal obstruction, which is mostly seen in the upper rectum and is mostly incomplete obstruction. Sometimes, the obstruction may be temporarily relieved by shedding the necrotic tissue on the surface of the tumor, but the obstructive symptoms will appear again with further growth of the tumor.