Objective To study the damage of underwater explosion to the brain and lung of beagles in the swimming battle position. Methods Twenty healthy beagles were evenly randomized into 4 experimental groups (5 m, 8 m, 11 m or 15 m away from the explosion source) and a control group (n=4). Beagles in water were subjected to the explosion of 1 kg 2,4,6-trinitrotoluene (TNT) equivalent bare explosive 2 m underwater. Underwater and intracranial pressure sensors and high-speed camera were used to record the process of explosion injury. Computed tomography (CT) scans of the head and chest, as well as magnetic resonance imaging (MRI) scans of head were performed 3 h after the explosion. Brain and lung specimens were taken 24 h after the explosion, and injuries of them were observed. Hematoxylin-eosin (H-E) staining and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) staining were performed afterwards to observe the histopathological changes and apoptosis of brain and lung tissues. Results The records of pressure sensors and high-speed camera showed the injury process of underwater explosion included 2 stages:blast wave and bubble pulsation. There were 4, 3, 1 and 0 beagles died in 5 m, 8 m, 11 m and 15 m groups, respectively. The head CT and MRI showed that there was no obvious brain injury in the experimental groups, while the chest CT showed that there were intrapulmonary hemorrhage, pneumothorax, hemothorax or pleural effusion. H-E staining showed that there were no obvious changes in the brain tissue of beagles in the experimental groups, but the alveoli were ruptured, and there were a large number of red blood cells in the alveolar cavity, and many inflammatory cells infiltrated in the lung interstitial. TUNEL staining showed only a few positive cells in the hippocampus, while the alveolar epithelial cells and interstitial cells in the lung showed a trend of extensive apoptosis and necrosis. Conclusion The main injury caused by underwater explosion to beagles in swimming battle position is lung blast injury, while the brain tissue injury is relatively slight.