The prognosis of colorectal cancer is closely related to early diagnosis, most early cancers can be cured, and endoscopy is the main means of early diagnosis. The main target population alarm signals for colonoscopy screening include all people with blood in stool, black stool, anemia and weight loss. The high-risk groups in our guidelines: 1. positive occult blood in stool, 2. history of colorectal cancer in first-degree relatives, 3. previous history of symptomatic intestinal adenocarcinoma, 4. history of cancer in person, 5. change in stool habit, 6. any 2 of the following: chronic diarrhea, chronic constipation, mucus and blood stool, chronic appendicitis or history of appendectomy, chronic cholecystitis or history of cholecystectomy, long-term mental depression. There are alarm signals. The general risk group screening is for people aged 50 to 74 without alarm symptoms of colorectal cancer. Once early tumors and precancerous lesions such as polyps are detected, immediate surgery is performed to kill the tumors in the cradle. Finding one case of early cancer saves a family.