Colorectal cancer is a common tumor. Since the incidence of colorectal cancer may be related to high-fat and low-fiber diet, the incidence rate is higher in developed countries, and the incidence rate in China has also increased in recent years. Like any malignant tumor, early detection and early treatment is the only way to improve the long-term survival rate of colorectal cancer, for example, according to Dukes stage, the 5-year survival rate can reach 90±% for stage A, 75±% for stage B, less than 50% for stage C and less than 10% for stage D, which shows the importance of early diagnosis and treatment. The so-called early stage generally refers to Dukes A stage. T1 means the tumor only invades the submucosa, T2 means the tumor invades the intrinsic muscular layer, if it crosses the muscular layer to the subplasma layer, it belongs to stage B. Since early stage carcinoma like T1 still has 10% local lymph node metastasis, in recent years, more attention has been paid to the study of mucosal carcinoma in situ, which is called mucosal internal or mucosal carcinoma in Japan. This kind of early stage carcinoma has no lymph node metastasis and can be completely cured, but it requires high magnification endoscopy or special fluorescence and genetic examination techniques to be detected, so it is still difficult to be used in clinical practice generally. If Dukes A stage cancer is detected, the cure rate can be greatly improved, but the number of patients with Dukes A stage cancer is only a small number in clinical practice, according to the data of our hospital since 1994, Dukes A stage cancer is only about 16% of all hospitalized colorectal cancer patients, which means that the diagnosis of early colorectal cancer is still a problem that has not been properly solved. If patients come to the doctor only when symptoms appear, it is obvious that it is not early stage. Early detection of colorectal cancer should start with the high-risk group. As far as we know, those with family history of colorectal cancer have 2-3 times higher chance of developing colorectal cancer than the general population. Those who have adenocarcinoma polyps or history of polyp surgery have 2 to 5 times higher chance of cancer than those who do not have polyps, and the incidence of cancer in multiple cases is 1 times higher than that in single cases. Those with a history of colorectal cancer surgery have a 3 times higher chance of developing a second primary cancer of the colon than the general population. In addition, gynecological patients with a history of radiation therapy, those who have had breast cancer, and those with long-term chronic inflammation of the colon have a higher chance of developing colorectal cancer than the general population. Generally speaking, if middle-aged and elderly people over 40 years old have unexplained change in stool habit or abnormal stool, they should never take it lightly and must undergo further examination to avoid delaying the diagnosis.