Objective To investigate the effect of 40 m hyperbaric air exposure on brachial artery function of divers. Methods Five divers were enrolled and exposed to hyperbaric air with a maximum pressure of 40 m for a total of 190 min. The brachial artery diameter, systolic peak velocity (SPV) and resistance index (RI) were measured by Doppler ultrasonography before and after hyperbaric air exposure, and flow-mediated dilation (FMD) was calculated to evaluate the effect of hyperbaric air exposure on brachial artery function. Results Compared with before hyperbaric air exposure, the brachial artery diameter was decreased (P＞0.05), RI and FMD were increased slightly (P＞0.05), while SPV was decreased significantly (P＜0.05) after hyperbaric air exposure. Conclusion Exposure to hyperbaric air at 40 m can lead to brachial artery contraction, increase resistance, and decrease flow velocity, but it has a slight impact on the brachial artery function, with no significant change in FMD.