Current cesarean section in domestic and overseas often chooses spinal anesthesia. And in order to avoid the impact of drugs on the fetus, before the delivery, anesthesiologist generally don't use sedative or analgesic drugs. However, the majority of puerperas would appear nervous, anxiety, fear and other psychological reactions in cesarean section, and thus produced a series of stress reactions that not only cause the hemodynamic fluctuating in anesthesia and operation, but also lead to different degrees of personality and behavior changed. It causes serious injury to physical and mental health of patients. Dexmedetomidine is a highly selective α2 receptors agonist (α2-AR) ，it has sedation, analgesia, antisympathetic pharmacological effects and unique "conscious sedation" without respiratory depression. At present, dexmedetomidine has been widely used in patients in clinics and clinical anesthesia, it has been hailed as an"dvocate medicine in modern comfortable anesthesia."Experiments in animals have shown that dexmedetomidine had no adverse effects on pregnant rats. In addition, Dexmedetomidine has successful application in preterm infants, infants and children anesthesia, also has a few for caesarean patients sedation reports. Although the placental transfer and the foetal metabolism of dexmedetomidine have been reported and the result show no adverse effects on neonates, but the placental transfer of dexmedetomidine in intravertebral anesthesia area was lack of systematical research.