In order to clarify whether the anus can be preserved or not, what tests do patients need to do before surgery? First of all, the distance from the tumor to the anus should be checked, and the size and stage of the tumor should also be checked. So the corresponding examinations are rectal diagnosis and proctoscopy. To determine the size, invasion level and lymph node metastasis of the tumor, MRI, pelvic ultrasound and CT should be done. But the most critical thing is to ensure the clean cut edge and early stage of the tumor (especially for stage I patients), so that the recurrence rate is very low and low. The most critical thing is early detection and good differentiation of the tumor.