The following groups are at risk and should be reviewed regularly: 1. family history; 2. age >45 years; 3. patients who have undergone cholecystectomy; 4. autistic personality; 5. habitual constipation; 6. unexplained weakness, anemia and lack of energy; 7. change in stool habits and traits. Early stage colorectal cancer refers to cancer confined to the mucosa and submucosa, regardless of its size or the presence or absence of lymph node metastasis. Some people classify colorectal cancer that infiltrates the muscular layer but does not penetrate the plasma membrane layer and has no local lymph node metastasis as early stage colorectal cancer. Histologically, early colorectal cancer is divided into intra-mucosal cancer (m cancer) and submucosal cancer (sm cancer), and the latter can be subdivided into sm1, sm2 and sm3. Paying attention to high-risk groups, regular follow-up and close observation can help detect early colorectal cancer. The main methods to diagnose early colorectal cancer are barium enema by X-ray and endoscopy. Pigmented endoscopy method, magnified electronic endoscopy, ultrasound endoscopy and 3D endoscopic diagnostic system have been used in clinical practice. Endoscopic early colorectal cancer can be divided into augmented type and flat type. The former can be divided into tipped and non-tipped; the latter can be divided into flat elevated type and flat depressed type. Recently, a new type of superficial growth tumor (LST) has been proposed.