Objective: To comparatively study the effects and mechanisms of b-blast combined injury and b-firearm combined injury complicated with seawater immersion on vascular endothelial cells. Methods: A total of 40 healthy adult hybrid dogs of both sexes, weighing 12-15 kg, were used in this study. Randomly-selected 20 dogs were established as models of b-blast combined injury (the b-blast injury group) and the other 20 dogs as models of b-firearm combined injury (the b-firearm injury group). Then the wounds of all the dogs were immediately immersed in seawater for 4 hours, and then they were taken out from the seawater. Blood samples were withdrawn from the central vein of the dogs before injury, and at 4, 7, 10, 20, and 28 hours after injury to measure the circulating endothelial cells and the von Willebrand factor. Results: Circulating endothelial cells increased significantly at 4 hours after injury in all the dogs. But they reached peak at 7 hours after injury in the b-blast injury group and at 28 hours after injury in the b-firearm injury group. The changes of circulating endothelial cells in the b-blast injury group were significantly different from those in the b-firearm injury group at 4, 7, 20, and 28 hours after injury (P<0.01). The von Willebrand factor reached peak at 4 hours after injury in the b-blast injury group and at 28 hours in the b-firearm injury group. The changes of von Willebrand factor in the b-blast injury group were significantly different from those in the b-firearm injury group at 4, 20, and 28 hours after injury (P<0.01).Conclusions: In b-blast injury combined with seawater immersion, the vascular endothelial cells changed most significantly at 4 hours or 7 hours after injury, while b-firearm injury combined with seawater immersion have the same at 20 hours or 28 hours after injury.