Objective To explore the effect of first intensive hyperbaric oxygen therapy on severe acute carbon monoxide poisoning (ACMP) patients.〖WTHZ〗Methods A retrospective analysis was conducted in 81 patients with severe ACMP.According to the treatment schedule, the patients were randomly divided into 2.2ATA intensive hyperbaric oxygen(HBO) treatment group and 20ATA HBO pressure group for the first time. The awakening time after HBO, whether or not delayed encephalopathy and the prognosis after 90 days after HBO in the two groups were analyzed.Results81 patients with severe ACMP were enrolled in the study. 36 patients (44.4%) were in the experimental group using 2.2 ATA for the first time and 45 patients (55.6%) in the control group using 2.0 ATA for the first time. There was no significant difference in gender, age and poisoning mode between the two groups. The percentage of awakening within 24 hours in the experimental group was significantly higher than the control group (83.3% vs53.3%, P=0.004). The incidence of delayed encephalopathy in the experimental group was lower than the control group (19.4%, vs42.2%, P= 0.029). The total number of HBO therapy and the prognosis after 90 days between the two groups didn′t find significant difference. Conclusion For severe ACMP patients, the first intensive hyperbaric oxygen therapy could shorten the time of consciousness disturbance, and reduce the incidence of delayed encephalopathy.