Colorectal cancer is one of the common malignant tumors of the gastrointestinal tract. In western economically developed countries, for every 25 babies born, 1 will suffer from colorectal cancer later. In China, the incidence of colorectal cancer has increased year by year in the past 20 years due to factors such as changing dietary habits, and about 47,500 people die from colorectal cancer every year nationwide. What exactly causes colorectal cancer? Research shows that diet, environment, genetics, race and other factors are related to the development of colorectal cancer. The dietary factors and environmental factors are more important. Take Japan as an example, in the 1950s, Japan was the same as China, which was a country with low incidence of colorectal cancer. With the economic recovery and development after the war, the incidence and mortality rate of colorectal cancer in Japan has been increasing. According to the Japan Cancer Society, from 1947 to 1978, the mortality rate of colorectal cancer increased approximately two times, while various other cancers such as lung cancer only increased by 60%, and stomach cancer and cervical cancer decreased by 30% and 60% respectively. The reasons for this are mainly the following: First, it is due to the increase of fat diet and decrease of fiber diet. The increase in the incidence of colorectal cancer in China’s cities in recent years is also related to the change in dietary structure. Secondly, the relationship between environment and colorectal cancer is very close. Environmental factors include: lack of selenium in the soil; the influence of schistosomiasis, which is also a high incidence area of colorectal cancer in China; and smoking, which can easily cause colorectal cancer. Thirdly, it is genetic factor. About 10% of colorectal cancer is related to genetic factors, so the offspring of patients diagnosed with familial colon polyposis, hereditary non-polyposis colorectal cancer and sporadic hereditary colorectal cancer should be closely tracked and followed up. Also, some benign tumors of the large intestine called polyps should not be ignored. People who have had ulcerative colitis for a long time also have a greater chance of developing colorectal cancer. In summary, people with one of the following conditions should be considered as a high-risk group for colorectal cancer: adults in areas with a high incidence of colorectal cancer, such as large cities and the southeast coast of China; patients with colorectal adenoma, family members with multiple familial adenomatosis; patients who have previously suffered from colorectal cancer; patients with schistosomiasis; family members of patients with colorectal cancer; members of cancer family syndrome; people who have received radiation therapy to the pelvis (some people have reported that after 1020 days of pelvic radiation therapy, they have a higher risk of cancer. It has been reported that 1020 years after pelvic radiotherapy are prone to rectal cancer); patients with chronic ulcerative colitis. It is believed that the chance of developing colorectal cancer is 10 times higher in people with this disease than in normal people.