Screening for colorectal cancer is divided into two cases, as follows: First, people without any discomfort should be screened for colorectal cancer, and the easiest and most economical way can be to do fecal occult blood test to see if there is blood in stool. Generally, blood in the stool will be visible to the naked eye only if the amount of bleeding in the stool is relatively large, while in the case of relatively small amount of bleeding, there is no way to distinguish it to the naked eye, and the fecal occult blood test can detect a small amount of bleeding in the stool. Second, people with family history of tumor or intestinal cancer, or people with some symptoms, such as constipation, diarrhea, alternating constipation and diarrhea, as well as blood in stool visible to the naked eye, intestinal obstruction, abdominal mass, anemia, wasting, etc., if they have the above symptoms, they need to pay special attention, and in addition to fecal occult blood test, they should also improve colonoscopy and abdominal CT examination to identify them.