ObjectiveTo systematically evaluate the effect of hyperbaric oxygen therapy on delayed encephalopathy caused by carbon monoxide poisoning.MethodsChina National Knowledge Infrastructure, Wanfang Data, CQVIP data, China Biology Medicine Database, PubMed, Embase, and Cochrance Library were searched by computer for randomized controlled trials on hyperbaric oxygenation for delayed encephalopathy caused by carbon monoxide poisoning which were published in English or Chinese from the dates of establishment of the databases to March 31st, 2019. After literature including, excluding, and screening, RevMan 5.2 software was used to conduct a meta-analysis.ResultsA total of 25 studies were included, including 1 797 patients, 924 in the hyperbaric oxygen therapy group (the trial group) and 873 in the control group. The clinical effective rate [relative risk (RR)=1.24, 95% confidence interval (CI) (1.19, 1.30), P<0.000 01], the normal rate of electroencephalogram [RR=2.10, 95%CI (1.18, 3.75), P=0.01], the Mini-Mental State Examination score [standard mean difference (SMD)= 3.19, 95%CI (2.06, 4.32), P<0.000 01], and the Activities of Daily Living score [SMD=1.46, 95%CI (1.02, 1.90), P<0.000 01] were all higher in the trial group than those in the control group.ConclusionHyperbaric oxygen therapy for delayed encephalopathy caused by carbon monoxide poisoning can improve symptoms.