Recently, we met a young rectal cancer patient, in his early 30’s, it is a pity that he is in his prime of life and has just taken up a leadership position. The anatomical structure of the anorectum, the dentate line is a very important structure. To distinguish internal hemorrhoids, external hemorrhoids and mixed hemorrhoids, etc., we must clearly grasp the anatomical position of the dentate line and related concepts. The dentate line is a serrated line where the skin of the anal canal joins the rectal mucosa. 85% of anorectal diseases can occur near the dentate line, which is clinically important. 1, the line of demarcation of the endo-epidermis: the dentate line is the place where the embryonic endo- and ecto-epidermis meet, so almost all anal and rectal congenital malformations such as lockjaw occur in the dentate line. 2.The combination line of anal canal and rectum: above the dentate line is the rectum, which is about 12 to 15 cm long, and below is the anal canal, which is about 1.2 to 1.5 cm long in adults. 3, the migration line of mucosal skin: the dentate line is where the embryonic endoderm and ectoderm meet, so almost all congenital malformations of the anus and rectum, such as lockjaw, occur in the dentate line. 4.Divisions of the nerves of the organism: The nerves above the dentate line are vegetative nerves and have no obvious pain, so internal hemorrhoids are not painful and are painless zones during surgery; the nerves below the dentate line are spinal nerves and have sensitive pain, so external hemorrhoids and anal fissures are very painful and are painful zones during surgery, and all painful anal diseases are below the dentate line. 5.Venous and lymphatic up and down the shunt: The blood vessel above the dentate line is the superior rectal blood vessel, and its vein is connected with the portal vein system; below the dentate line is the anal blood vessel, and its vein belongs to the inferior vena cava system. Near the dentate line, the portal vein communicates with the corporal vein. The lymph above the dentate line flows back upward and converges into the pelvic lymph nodes; the lymph below the dentate line flows back downward and converges into the abdominal lymph nodes through the root of the thigh. Therefore, the tumor metastases above the dentate line to the abdominal cavity and below the dentate line to the root of the thigh. When the feces reaches the anal canal from the rectum, the nerve endings receptors in the dentate area will be stimulated, which will reflexively cause the internal and external sphincter to diastole and the levator muscle to contract, causing the anal canal to open and the feces to be discharged. If the dentate line is removed during surgery, the defecation reflex will be weakened and constipation or sensory incontinence will occur.