Abstract： Objective:To explore the mechanism of hyperbaric oxygen (HBO) therapy on improving neurological function recovery of traumatic brain injury (TBI) patients through observing the effects of HBO on peripheral blood regulatory T cell (Treg) ratio, neuron specific enolase (NSE), and hypersensitive C-reactive protein (Hs-CRP) in TBI patients.Methods:After signing the informed consent, 68 patients with severe TBI were divided into the control group (30 cases) and the HBO group (38 cases). The patients in the control group were treated with emergency decompression of bone flap + intracranial hematoma removal, postoperative oxygen inhalation, hemostasis, reduction of intracranial pressure, improvement of brain circulation, and brain metabolism, neurotrophic and other conventional treatments. The HBO group patients were treated with HBO on the basis of the treatments of the control group. The score of the Glasgow coma scale (GCS) and the levels of peripheral blood NSE, Hs-CRP, and Treg were measured before and after treatment for 7 d and 14 d.Results:After 14 days of treatment, the GCS score of the HBO group was significantly higher than that of the control group, with statistically significant difference (9.7±2.8 in the HBO group and 7.9±2.2 in the control group, P<0.05). After treatment 7 d and 14 d, the serum HS-CRP expression [7 d, (1.45±0.44) ng/ml; 14 d, (0.99±0.39) ng/ml], CD4 + CD25 + T cells [7 d, (10.8±3.7)%; 14 d, (7.1±3.0)%] and CD4 + CD25high + CD127dimT cells [7 d, (6.0±2.6)%; 14 d, (3.5±2.2)%] were significantly lower than those of the control group [HS-CRP, (1.78±0.52) ng/ml on 14 d, (1.30±0.50) ng/ml on 14 d; CD4 + CD25 + T, (12.9±4.7)% on 7 d and (9.8±3.5)% on 14 d; CD4 + CD25high + CD127dimT, (7.4±2.7)% on 7 d and (5.2±2.2)% on 14 d, the differences were statistically significant ( P<0.05). Only 14 days after HBO treatment, the difference of the serum NSE expression between the two groups was statistically significant (the HBO group: 12.67±2.84, the control group: 16.3±2.67, P<0.05). Conclusion:HBO treatment can significantly promote the recovery of neurological function in TBI patients. HBO therapy may reduce the neuroinflammatory response after TBI by changing the proportion of Treg cells in peripheral blood, thus reducing neuron damage and promoting neurological function recovery.