Tearing of the mucous membrane at the entrance of the vagina due to external force and bleeding. It is a severe trauma to the soft tissues between the anus and external genitalia, resulting in a visible tear in the perineum from localized bulging and thinning, and in severe cases, even tearing into the anus. So, what phases are needed to identify a tear in the mucosa of the vaginal entrance? The causes of the tear should be identified. 1, delivery too fast: in the primigravida, the vagina and perineum of the complete expansion of a certain process, such as delivery too fast, the vagina and perineum too late to adapt to the occurrence of cracks. 2, the fetal head is too large or fetal head position: fetal head is too large, fetal head position is not as the face first exposure or persistent occipital posterior position delivery, can be due to the long diameter line and perineal laceration, and such as shoulder dystocia, i.e., delivery of the fetal head, fetal shoulder delivery difficulties, can occur in the process of assisted delivery of laceration. 3, perineum local anatomical factors: perineum is too long or too hypertrophic, or the original scar formation can make the vagina and perineum laceration, and also such as the pubic arch angle is too small, the position of the fetal head delivery downward, the perineum is overstretched is also the cause of rupture. 4, poor delivery techniques: such as insufficient estimation of the course of labor and rushed into action, delivery personnel arbitrarily in the bottom of the uterus pressure, protection of the perineum did not pay attention to make the head of the fetus fully bent, can occur perineal laceration. Especially for the first time for the perineal incision, the cut is too small or the angle of the cut is too small can occur tear, and even easily lead to Ⅲ degree of laceration. 5, surgical delivery: obstetrics transvaginal surgical delivery are aimed at assisted delivery, no matter forceps, fetal head attractor, breech traction or assisted delivery, its operation in the delivery of the fetal head should be in line with the requirements of the normal delivery from prone flexion to supine extension, such as the operation speed is too fast, the direction of the mastery of the direction is not good, can cause laceration.