Sailed placenta is aggressive, but if it is correctly diagnosed before delivery and cesarean section is chosen before rupture of membranes, fetal mortality can be reduced. There are many diagnostic tools available for the diagnosis of sail-like placenta, but all have their own advantages and disadvantages. Smear of vaginal bleeding: In case of suspected rupture of anterior vascularization in combination with placenta previa, if the bleeding is very small, a vaginal blood specimen can be collected for smear, and if nucleated red blood cells or juvenile red blood cells are found, the diagnosis can be made after excluding the mother’s primary disease (blood disease, etc.). However, in the case of heavy bleeding, it is difficult to make a diagnosis in a short period of time because of the rapid progression of the disease. Transvaginal palpation: In the case of placenta previa, fixed vascular pulsations in the amniotic membrane can be palpated vaginally at a frequency consistent with the fetal heart rate. If amnioscopy is performed at the same time, the result is more reliable, but it is invasive, expensive and technical, and difficult to be carried out universally. Ultrasonography: With the widespread use of color ultrasound in prenatal diagnosis and the improvement of ultrasonographers’ understanding of membranous placenta, ultrasonography has become the most commonly used and the easiest and most reliable method to diagnose membranous placenta. Ultrasound characteristics of sail-shaped placenta: 1. The attachment point of umbilical cord and placenta cannot be found on the fetal side of the placenta. 2. 2, in the placenta outside the free fetal membrane can be seen in the flat walking multi-branched umbilical blood vessels echo, vascular pulsation and fetal heart rate, along its course can be traced to the umbilical cord attachment point, in the spot observation, can be found that the umbilical blood vessels into the fetal membranes after the fan-shaped separation, no spiral structure. In 3, when the sail-shaped placenta is combined with vascular antecedent, the blood flow signal of umbilical blood vessels can be found above the endocervical os. One of the keys to ultrasound diagnosis is the site of umbilical cord attachment. Some studies have found that prenatal ultrasound purposefully observes the placental cord attachment site, which can improve the display rate of abnormal cord attachment, and the diagnostic accuracy rate can reach 91%. Therefore, systematic prenatal ultrasonography with purposeful observation and display of the umbilical cord attachment site is of great significance for prenatal detection and diagnosis of sail-shaped placenta.