Carbon monoxide poisoning (commonly known as gas poisoning) is an asphyxiating gas produced by incomplete combustion of carbon-containing substances. As carbon monoxide takes over the hemoglobin in the blood, it takes the place of oxygen and causes hypoxia in the body. This results in a series of symptoms and cerebral hypoxic sequelae due to lack of oxygen. Such as severe headache, nausea, vomiting, and coma in severe patients, even for several days. There are also patients who cannot wake up. In severe cases, after resuscitation and clarification of consciousness, a delayed encephalopathy of carbon monoxide poisoning with dementia and increased muscle tone and tremors occurs after 10-30 days (pseudo-healing period). The clinician can diagnose the patient’s condition based on the patient’s history, symptoms, signs and imaging features. In addition, hyperbaric oxygen therapy can make the carbon monoxide excreted from the body as soon as possible, and the hyperbaric oxygen therapy for comatose patients can reduce the sequelae and the incidence of late onset encephalopathy. This point has been agreed in domestic and international clinical studies. Nevertheless, there are still 10-30% of patients with delayed onset encephalopathy. This is related to patients with hypertension, diabetes mellitus, and cardiovascular disease. Careful clinical observations have shown that psychological trauma is an important factor leading to late onset encephalopathy in patients with severe carbon monoxide poisoning after clarity of consciousness. Patients with carbon monoxide poisoning coma and delayed onset encephalopathy are either confused or severely demented, and their survival is completely dependent on medical personnel and medical facilities. Early, scientific, rational and comprehensive treatment is important for the outcome of treatment. It is not only hyperbaric oxygen therapy, but also includes assessment of their general condition, meticulous care, adequate nutrition, reasonable intake and calories, electrolyte and acid-base balance, maintenance of proper posture, rehabilitation guidance, etc. According to statistical reports, the rate of improvement and cure of severe carbon monoxide poisoning, the incidence of late onset encephalopathy and the rate of improvement of late onset encephalopathy of carbon monoxide poisoning in the hyperbaric oxygen department of Chaoyang Hospital are higher than those in developed countries in Europe and America.