Rectal cancer invades to the outer membrane layer, which generally means that the tumor invades to the plasma membrane layer, indicating that the depth of tumor invasion is larger. Rectum can be divided into mucosa, submucosa, muscularis propria and epimysium or called plasma membrane layer in terms of anatomical structure. With the progression of disease, rectal cancer will gradually invade to the outer rectum, rectal cancer invades to the outer membrane layer, according to TNM staging criteria, suggesting that the tumor enters into T3 stage, which can be combined with regional lymph node metastasis as well as distant metastasis. Combined with the specific pathological type and clinical stage of the patient, surgery, chemotherapy, radiotherapy and other treatment modalities can be chosen accordingly. It is recommended that rectal cancer patients should seek medical treatment in time, do further examination under the guidance of clinicians, and do standardized treatment after clarifying the condition.