Rectal finger examination is still the most basic and important examination method among the series of pre-surgical examinations for rectal cancer. Many diseases of the anus and rectum can be diagnosed by the finger, especially since 80% of rectal cancers occur within the reach of the finger. The doctor will apply paraffin oil to the finger sleeve for lubrication before performing the finger examination, then massage the sphincter and slowly enter the anus. This is a normal reaction. The patient should not be nervous and can take deep and long breaths to relax the anus and cooperate with the doctor’s examination. Laboratory tests Stool occult blood test is simple and easy to perform, and it is the initial screening method for colon cancer screening and routine examination of colon diseases. Immunological methods can also be applied to improve the correct rate if available. Endoscopy Any clinical manifestations such as blood in stool, mucus stool, pus stool, chronic diarrhea, thin stool strips, etc. with unknown causes and no abnormal findings by rectal examination should be routinely examined by sigmoidoscopy or fiberoptic colonoscopy. Endoscopy can observe the lesion under direct vision and take biopsy for pathological diagnosis. It is important for the early diagnosis of lesions (tumors, polyps, ulcers and inflammation) in the rectum and lower sigmoid colon. Fiberoptic colonoscopy is currently the most effective, safe and reliable examination method for the diagnosis of lesions in the large intestine, and most early colorectal cancers can be detected by endoscopy. The application of total colonoscopy is an important development in gastroenterology, which has significantly improved the diagnostic rate for the detection of large bowel diseases as well as diseases including terminal ileocecal part, and non-surgical treatments such as polypectomy removal, hemostasis, and sigmoidoscopic torsional repositioning have been performed by electronic display colonoscopy. Double contrast imaging Traditional barium enema X-ray examination often has difficulty in showing early cancer and colorectal adenoma, while air-barium double contrast imaging technology has greatly improved the detection rate and diagnostic accuracy of early colorectal cancer and small adenoma, and has now become a routine examination in radiology. CT diagnosis CT can not be used as a method of early diagnosis, but it is of great significance for the staging of colon cancer, especially for patients who are estimated to be inoperable but may be surgically resected after the application of external radiation or local intracavitary radiotherapy, and it is of great significance for the surgical estimation of advanced rectal cancer and recurrent rectal cancer. It can directly observe the tumor invasion of pelvic muscles (levator muscle, internal ossier muscle, coccygeus muscle, pear muscle, gluteus muscle) bladder and prostate. CT examination of the pelvis can be performed at 3 months after surgery as a base film for follow-up. CT should be performed every 6-8 months for 2 to 3 years after surgery or repeated when CEA is elevated. in addition, CT can provide correct localization and determine the appropriate target volume for the application of radiotherapy to recurrent rectal cancer. Ultrasonography Endorectal ultrasonography is a new diagnostic method to detect the invasion of rectal cancer and the degree of tumor infiltration into the rectal wall, and has been used in clinical practice since 1983. Endorectal ultrasonography can correctly diagnose the location and size of tumor invasion. Magnetic resonance examination Some researchers claim that magnetic resonance examination (MRI) is more meaningful than CT for the external invasion of rectal cancer. However, there are still many technical problems in MRI that need to be improved, and the understanding of the image provided by MRI needs to be further deepened, and the cost of MRI is also an obstacle to its wide application compared with intracavitary ultrasonography.