Colonoscopy can detect colon and rectal cancer. It is the most important and primary method for examining colonic mucosal lesions. The large intestine includes the cecum, colon, and rectum. Colonoscopy allows direct visual inspection of lesions, including the size and color of the lesions, and whether there are ulcers and erosion, the nature of any attachments, etc. It also allows for direct biopsy. Firstly, it can assess the texture of the lesion, such as whether it is soft, hard, or brittle. Moreover, the biopsied sample can be analyzed histologically to determine the benign or malignant nature, depth of infiltration, etc. Different pathological characteristics have different prognoses and treatment methods, suitable for early cancers treatable under endoscopy, or those that can be removed during the process of the colonoscopy.