Abstract: The cerebral hemodynamic disorders are most likely to occur in preterm infants, especially in extremely preterm infants with gestational age <28 weeks, due to the immaturity of cerebral vascular development and poor autoregulation of cerebral blood flow. Also the neurons, oligodendrocytes and their precursors in preterm infants are abnormally sensitive to hypoxia and ischemia with low tolerance and high vulnerability, which lead to a higher incidence of brain damage and neurological sequelae in preterm infants than that in full-term infants. Because brain injury in the premature often lacks the obvious nervous system symptom and the sign clinically, it is easy to be misdiagnosed and hence suitable treatment opportunity is missed. Cranial ultrasonography, MRI and EEG are the special examinations for early diagnosis of brain injury in preterm infants. In the diagnosis of early intracranial hemorrhage, cranial ultrasonography is superior to both MRI and EEG, but MRI especially DWI has the highest diagnostic value in the evaluation of leukoencephalomalacia, and EEG plays a supporting role in diagnosis of brain injury in each period. The three techniques have their own advantages and disadvantages. In clinical practice, if three techniques can be rationally used for the diagnosis of brain damage in preterm infants, it would be helpful to detect the disease in time and treat appropriately as soon as possible, and thus reduce the neurological sequelae and disability in preterm infants, and improve the long-term prognosis.