Colorectal cancer is a malignant tumor that seriously threatens the life and health of human beings, and its incidence rate ranks the 3rd among all kinds of malignant tumors. In recent years, with the development of economy and the improvement of living standard of our people, the incidence rate of colorectal cancer shows the trend of increasing year by year. (I) Risk factors of colorectal cancer: including genetic and environmental aspects. (1) Familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC): less than 1% of colorectal cancers are related to FAP, while HNPCC accounts for 2%~6% of colorectal cancers. According to statistics, 90% of patients with untreated FAP have colon cancer at the age of 45, while HNPCC is also characterized by low age of onset, with a median age of onset of 48 years old, and some patients have onset of the disease at the age of 20 years old. Personal or family history of sporadic colorectal cancer and adenomatous polyps: 1.5%~3.0% of colorectal cancer patients develop a second primary colorectal cancer within 5 years after surgery. Patients with a history of adenomatous polyps or villous/mixed adenomas over 1 cm in diameter also have a significantly higher incidence of colorectal cancer than the general population. Another study shows that the risk of colorectal cancer is 1.7 times higher than that of the general population when there is a colorectal cancer patient in the immediate family, and the risk is further increased when the age of onset of the disease is less than 55 years old or when there are two onset of the disease in the immediate family, and a family history of colorectal adenomatosis is also significant in increasing the risk of colorectal cancer. Inflammatory bowel disease: ulcerative colitis with the prolongation of the course of the disease and the expansion of the scope of the lesion and its colon cancer incidence increases. The risk of colon cancer in total colitis is 5-15 times higher than that in the general population, and the risk in patients with left hemicolonic lesions is 3 times higher; it is estimated that the incidence of colon cancer in patients with ulcerative colitis with a disease duration of 10-20 years is 0.5%, and then it increases to 1%. 4, diabetes and insulin resistance: the results of a meta-analysis showed that the incidence of colorectal cancer in diabetic patients was 30% higher than that in nondiabetic patients among 2,593,935 participants, and the possible mechanism is that insulin is an important growth factor for colonic mucosal cells, which has a certain stimulating effect on colonic tumor cells. 5, alcohol consumption: a pooled analysis of eight independent studies showed that alcohol consumption can moderately increase the risk of colorectal cancer, especially when daily alcohol intake exceeds 45 grams. The increased risk of colorectal cancer may be related to the fact that alcohol interferes with the intake and absorption of folic acid. 6, obesity: at least two large prospective studies have shown that the risk of colorectal cancer is 1.5 times higher in obese than in normal-weight people. 7.Others: such as smoking, high intake of red meat and fat, pelvic radiotherapy, ileus instead of bladder. (II) Prevention of colorectal cancer: Inhibit the cancerous process of normal cells by reducing and eliminating pathogenic factors of colorectal cancer. 1. Dietary adjustment ① Reduce energy intake: energy intake is related to the occurrence of colorectal cancer. Most of the researches show that total energy intake is related to the risk of colorectal cancer, no matter the energy intake is protein, fat or carbohydrate. Reducing energy intake has the potential to reduce the incidence of colorectal cancer. ② Reduce fat and red meat intake: colorectal cancer is closely related to animal fat and meat, and some studies show that the risk of colorectal cancer in people with high fat intake is 3.26 times higher than that of people with low fat intake. And the intake of red meat in meat is a strong risk factor for colorectal cancer development. Reducing the fat content in food, especially minimizing the consumption of brown meat after frying and grilling, can help reduce the chance of colorectal cancer. ③Increase fruits, vegetables and dietary fiber: Fiber can increase the amount of feces, dilute carcinogens in the colon and adsorb bile acid salts, thus can reduce the occurrence of colorectal cancer. Epidemiological data show that the risk of colorectal cancer in those with the highest fruit and vegetable intake is only half of that in those with the lowest. Therefore, in the usual diet, we should try to consume more vegetables, fruits, fiber and reasonable diet to reduce the occurrence of colorectal cancer. ④ Vitamins and trace elements: some studies show that supplementation of vitamins A, C and E can transform the overgrowth of colonic epithelium in patients with adenomas to normal, but the current information does not support the use of antioxidant vitamins to prevent colorectal cancer. Folic acid reduces the incidence of colorectal cancer, but the exact mechanism is not known. Another study found that increasing calcium and magnesium intake may be able to reduce the incidence of colorectal cancer, but the current study is not very detailed. ⑤ Dietary anticarcinogens: dietary garlic, onions, leeks, scallions contain thioethers; citrus contains terpenes; grapes, strawberries, apples contain phytol as well as carrots, dioscoria, watermelon contains carotenoids, are considered to be able to inhibit mutations, with anticancer effects. Especially garlic, some research shows that garlic is the strongest protective effect and make people free from distal colon cancer vegetables. 2. Change life habits ①Exercise: obesity, especially abdominal obesity, and too little physical activity are the risk factors of colorectal cancer. Weight loss and exercise can prevent colorectal cancer. ② Abstain from alcohol and smoking. 3. Drugs Many epidemiological studies show that the incidence of colorectal cancer is reduced in those who take non-steroidal anti-inflammatory drugs (NSAIDs) for a long time. However, the dosage of NSAIDs, the duration of use, and the side effects caused by long-term application need to be further studied. Treatment of precancerous lesions Patients with ulcerative colitis, personal or family history of colorectal cancer or adenoma have higher risk of colorectal cancer. Through screening and follow-up, early removal of adenoma and treatment of colitis can reduce the incidence and mortality of colorectal cancer. Especially for those with a family history, screening high-risk individuals for colonoscopy through genetic testing is an important aspect of colorectal cancer prevention.