1, colonoscopy: ① sigmoidoscopy: straight and simple, the longest 30cm, easy to examine, can biopsy under direct vision, suitable for lesions below the sigmoid colon. ②Fiber colonoscopy: 120-180cm long, can be bent, can observe the whole colon, can make electrodesection, electrocoagulation and biopsy, can find early lesions. When the aforementioned examination is difficult to confirm the diagnosis, this examination can be done. 2.X-ray examination includes whole gastrointestinal tract barium meal examination and barium enema examination. The latter is appropriate for patients with colon tumor. Initially, the lesion may show stiffness of intestinal wall and destruction of phalloidin membrane, followed by giant filling defect and narrowing of intestinal lumen. For the discovery of smaller lesions, the intestinal cavity can be injected with gas for barium gas double contrast imaging for better effect. 3.B-type ultrasound and CT scan can not directly diagnose colon cancer, but they have certain value in determining the location, size and relationship between cancer and surrounding tissues, lymphatic and liver metastasis. 4.Serum carcinoembryonic antigen is not specific for colon cancer, and its positive rate is not sure. The high value is often related to tumor enlargement, and it can be restored to normal value more than a month after complete resection of colon tumor, and it can be increased several weeks before recurrence, so it is more significant to determine the prognosis.