Colorectal cancer is a common malignant tumor. In China, the incidence rate of colorectal cancer is second only to stomach cancer and esophageal cancer, and it is increasing rapidly at 4% per year. In some big cities, it has jumped to the second place of gastrointestinal tumors. The latest statistics show that the annual number of new cases of colorectal cancer in China is about 130,000 to 160,000, and the number of deaths is about 60,000 to 90,000. According to the registration of 12 counties and cities nationwide, the mortality rate of colorectal cancer has ranked 4th to 5th, although there has been great progress in the treatment of colorectal cancer. However, the 5-year survival rate of late-stage colorectal cancer has not improved much over the years. If detected and removed at precancerous lesions and early tumors, the mortality rate of colorectal cancer can be greatly reduced and the 5-year survival rate of colorectal cancer can be improved. According to authoritative research data, the 5-year survival rate of early-stage colorectal cancer can be over 90% after treatment, while the survival rate of late-stage colorectal cancer is less than 10%, so it is important to improve the early diagnosis rate. At present, the screening methods applied to large scale population are mainly fecal occult blood test, colonoscopy and biochemical immunological methods. Fecal occult blood is one of the characteristics of early colorectal cancer. Fecal occult blood test is simple, easy and inexpensive, and it should be performed once a year for people over 40 years old, and it is the most common primary screening method. The amount of bleeding in colorectal tumors is generally proportional to the volume of the tumor, but it is often intermittent. Certain diets can lead to false positives, so a controlled diet is required 2 days prior to the test, and 3 consecutive stool specimens are required, with two samples of each specimen tested, and one positive result is considered positive. Because any lesion that causes bleeding can lead to a positive result, it is not diagnostic of a tumor. Most tumors have slow intermittent bleeding, which makes the fecal occult blood test (FOBT) less sensitive. Increasing the number of specimens can increase the sensitivity, so continuous testing is recommended. Further testing should be performed after a positive result is found. Many prospective randomized trials have found that annual or biennial FOBT reduces mortality from colorectal cancer. Although fecal occult blood test can reduce the mortality rate of colorectal cancer, it does not change the biology of colorectal cancer and block the formation and transformation of colorectal neoplasms. In contrast, colonoscopy can detect lesions on the surface of the intestinal lumen, and in addition to biopsy of the lesions found, it can also perform microscopic removal of adenomas and early cancers. Most colorectal cancers start with adenomatous polyps, and the progression from adenoma to adenocarcinoma usually takes 7 to 12 years, which provides a good opportunity to detect and remove intestinal polyps in the population and prevent intestinal cancer. Colonoscopy can be used to remove adenomas, thus interrupting the process of adenocarcinoma, which is in a sense a primary means of colon cancer prevention. Of course, colonoscopy is relatively expensive, requires intestinal preparation, is painful, and its compliance is often unsatisfactory, so in China colonoscopy is only suitable for risk groups.