Hyperbaric oxygen (HBO) therapy and neural stem cell (NSC) transplantation can improve traumatic brain injury (TBI) clinically. This study aimed to investigate the mechanism of HBO promoting NSC proliferation and neurological recovery after TBI. Twenty-four Sprague–Dawley rats were divided randomly into three groups: a sham group, a TBI group (constructed using Feeney’s free-fall method), and an HBO-treated TBI group. Neurological function was evaluated by Neurological Severity Scores on days 1, 3, and 7, and we found that TBI-induced poor neurological function was improved by HBO. On day 7 after TBI, we observed that TBI promoted NSC proliferation, migration to the lesion area, and the levels of vascular endothelial growth factor (VEGF), VEGFR2, Raf-1, MEK1/2, and phospho-extracellular signal-regulated kinase (ERK) 1/2 protein, which were further boosted by HBO, from immunohistochemistry, immunofluorescence, and Western blot experiments. In vitro, cell injury was applied to NSCs isolated from neonatal Sprague–Dawley rats by the Cell Injury Controller II system. Moreover, data from the BrdU Kit and Western blot showed that in-vitro HBO significantly accelerated NSC proliferation and the levels of proteins related to cell cycle and the VEGF/ERK pathway after cell injury, which was suppressed by the VEGFR2 inhibitor. Taken together, this study indicated that HBO may promote NSC proliferation by activating VEGF/ERK signaling and play a crucial role in neuroprotection after TBI.