Colorectal cancer refers to malignant tumors occurring in the rectum and all of the colon (ascending colon, transverse colon, descending colon and sigmoid colon), and is one of the common malignant tumors in clinical practice. Due to the change of living conditions and habits, the incidence of colorectal cancer is on the rise, and the age of onset is mostly around 45 years old. The incidence of colorectal cancer accounts for about 12%-15% of the whole body malignant tumors. About 60% of cancers are located in the rectum, and the others are distributed in various colons. More than 80% of the cancers located in the rectum can be detected by rectal examination. The cause of colorectal cancer is generally considered to be the result of the synergistic effect of multiple pathogenic factors. Studies have shown that lifestyle changes and unreasonable dietary structure are closely related to the incidence of colorectal cancer: 1. Genetic factors, about 20% of colorectal cancer patients may play an important role in genetic factors. Among them, 10% are familial polyposis; and its molecular genetic basis has been found to be related to DNA replication errors, and relevant mismatch repair genes have been identified. 2, benign tumor malignant transformation, the most common benign tumor of the large intestine is polyps, polyps are mucosal tissue proliferation formed by superfluous organisms, mostly spherical. It is generally believed that it takes several years for adenomatous polyps to turn into cancer. The wider the base of the polyp, the greater the possibility of cancer, and the larger the polyp, the higher the cancer rate. 3. Inflammatory bowel diseases and chronic stimuli such as ulcerative colitis with extensive lesions, repeated destruction and repair of the intestinal mucosa, which is prone to carcinoma for more than 10 years, schistosome eggs, chronic diverticulitis and long-standing anal fistula, can induce cancer. Recently, some data show that hemorrhoids can also become cancerous after many years. Environmental factors, to some extent, are related to diet and nutrition, so diet is considered to be an extremely important factor: (1) High-fat, high-protein and low-fiber foods can increase the incidence of colorectal cancer. (2) Deep-fried, fried and baked foods and pickled products contain carcinogens, and certain other micronutrient deficiencies may also increase the incidence of colorectal cancer. Early colorectal cancer can be asymptomatic, and with the development of the disease, depending on the location of the lesion, different clinical manifestations will occur. For example, change in bowel habit or nature, increase in stool frequency, blood and mucus in feces, thinning of fecal sticks, painful sensation of falling and swelling in anus, urgency, constipation or diarrhea and abdominal pain, symptoms of intestinal obstruction, and systemic symptoms such as emaciation, weakness and anemia. Depending on the growth site and pathological type of cancer, the order of symptoms varies. Right half colon cancer mostly takes anemia, abdominal mass, abdominal pain, weakness and other systemic symptoms as clinical manifestations. Sudden blood in stool is seldom seen in medical treatment, and a few of them have symptoms such as constipation and frequent stools. Left colon cancer with blood in stool, mucus and frequent stools, causing intestinal obstruction is more common than right colon cancer, which may have symptoms such as abdominal pain and abdominal distension, and anemia is less common than right colon cancer. The early symptom of rectal cancer is change of fecal habits, that is, people who used to have regular feces become irregular, constipation or increased number of stools, feeling of incomplete discharge, and anal discomfort after stool. Later on, the symptoms include blood in stool, blood and mucus in stool, and with the development of the disease, rectal irritation symptoms, frequent bowel movements, frequent stools, anal drop, and posterior urgency. If the tissue is invaded, it may produce related symptoms. Patients with rectal cancer mostly have these symptoms and are often misdiagnosed as “chronic bacillary dysentery” and “enteritis”. Due to the lack of specific clinical manifestations of colorectal cancer, coupled with patients’ lack of awareness, poor self-care awareness or avoidance of medical treatment, the diagnosis is late. They often treat themselves with drugs as “dysentery, enteritis, hemorrhoids”, and only when they are ineffective do they consult internal medicine or surgery, while doctors are not highly alert to colorectal cancer or are influenced by the thinking of common diseases and multiple diseases in this department, which may also cause misdiagnosis. The prognosis of different pathological stages varies greatly, therefore, when there are the above symptoms, you should go to a gastrointestinal specialist for medical treatment and fiber colonoscopy if necessary to avoid delaying the disease.