Patients who are brain dead due to major brain diseases can be maintained for a certain period of time through support systems such as artificial respiratory muscles until cardiac arrest and circulatory failure; brain death due to extracerebral organ lesions such as heart and lung is not survivable. According to the diagnostic criteria of brain death in China, once a patient has the following conditions for more than 12 hours, and after the resuscitation is ineffective, and acute poisoning and endocrine diseases are excluded, brain death can be diagnosed: 1. the patient’s response to external stimuli disappears and he cannot move autonomously, but the spinal cord reflexes can survive; 2. the patient’s pupils are dilated and fixed, and the brainstem reflexes disappear completely; 3. the patient stops breathing autonomously and needs artificial ventilator to maintain ventilation; 4, EEG suggests no brain electrical activity in a straight line; 5, transcranial Doppler ultrasound suggests no cerebral blood perfusion phenomenon; 6, somatosensory evoked potentials suggest loss of brainstem function. Once brain death is diagnosed, it is irreversible and the patient’s life cannot be recovered. There is no effective method to prevent brain death, and the continuous use of support systems for brain dead patients will be a burden to families and society.