Ultrasound is rarely able to detect colorectal cancer. Ultrasound only has the advantage of scanning the lymph nodes in the corresponding area for the definite diagnosis of colorectal cancer to check whether there is metastasis. To thoroughly detect colorectal cancer, non-invasive CT or invasive colonoscopy is a very effective or accurate test, especially colonoscopy, which can find out the location, size and depth of infiltration of tumor, and if necessary, pathology can be taken under the microscope to reach the final diagnosis. To screen or detect colorectal cancer, it is best to choose colonoscopy for more effective and accurate diagnosis of colorectal cancer.