Objective To investigate the early physiologic and pathologic changes of primary explosive injury to brain in dogs.Methods Thirty mongrel male dogs were randomly divided into 13 mm detonated injury group (n=10),9 mm detonated injury group (n=10) and 5 mm detonated injury group (n=10); a spherical explosive with explosive energy of 1 g TNT was used to detonate at different distances (13,9 and 5 mm) to dogs' head to cause the severe,moderate and slight degrees of craniocerebral primary explosive injury in these dogs,respectively.Changes of respiratory frequency (RF),heart rate (HR) and mean arterial blood pressure (MABP),survival time and behavior in these dogs were observed; HE staining and electron microscopy were used to observe the pathological and ultrastructural changes of the brain tissues.Results The RF,HR and MABP levels after cerebral explosive injury were decreased in dogs of three groups; the decreased extent was increased following the increase of injury extent,with significant difference among the three groups (13 mm detonated injury group＞9 mm detonated injury group＞5 mm detonated injury group,P＜0.05).The server the injury,the more obvious the changes of dog behaviors (13 mm detonated injury group＞9 mm detonated injury group＞5 mm detonated injury group,P＜0.05).There were different extents of contusion and laceration of the brains,brain hemorrhage,and subdural hematoma in the three groups.Conclusions RF,HR and BP levels are decreased in three groups after cerebral primary explosive injury in dogs; the more obvious the physiologic and pathologic changes,the severer degrees of craniocerebral explosive injury.The severer injury dogs have more obvious behavioral changes.The survival time in dogs with the severer degrees of craniocerebral explosive injury is shorter than that in slight injury one.