The birth canal consists of the soft birth canal, which consists of the cervix, the lower part of the uterus, the vagina and the pelvic floor, and the bony birth canal, which is formed by the true pelvis. During labor, it is mainly the soft birth canal that is enlarged, while the shape and size of the bony birth canal do not change much. Before labor, the uterine isthmus forms the lower part of the uterus. After labor, the cervical canal gradually disappears, the uterine opening dilates, and the vagina is propped up by the prenatal part of the fetus and the anterior amniotic sac. After rupture of the membranes, the prenatal part of the fetus directly presses on the pelvic floor, so the soft birth canal forms a curved cylindrical channel, and at this time, the mucous membrane of the vaginal wall spreads out, the vagina widens, and the perineum thins out, so the fetus can pass through the birth canal without any problem. The ability to have a normal labor is closely related to whether the birth canal is normal or not. If there is any abnormality in the birth canal, the chance of difficult labor increases, and a cesarean section is needed. It is recommended that mothers go to regular hospitals to give birth, complete the relevant examinations before delivery, and follow the doctor’s instructions for a smooth delivery.