Abstract: The hemodynamic change of the internal carotid artery after craniocerebral fire-arm injury and its clinical significance are discussed. A steel ball was shot in the left frontal part with a musket at close range and a model of craniocerebral gunshot wounds is established in 17 hybrid dogs. The hemodynamic parameters of the right internal carotid artery was detected 30 min, 2h, 4h, and 6h before and after causing trauma, including Vp, Vd, Vm, RI and PI. Intracranial pressure and arterial pressure were dynamically observed in the interim. Intracranial pressure was evidently elevated compared to the pre-traumatic period (P<0.01), arterial pressure dropped (P<0.05) and internal carotid Vp, Vm and Vd lowered markedly (P<0.05) 30 min after trauma. RI and PI increased markedly and negative frequency spectrum appeared even in the early diastolic phase in 4 of the dogs whose intracranial pressure was elevated most markedly. RI and PI did not change markedly compared to the pre-trauma period in other 13 dogs. The internal vital signs kept more stable at all other time points and the hemodgnamic parameter stabilized at the first examination level after trauma. Internal carotid Vp, Vm and Vd after craniocerebral fire-arm injury lowered markedly. Owing to the influence of elevated intra cranial pressure and lowered arterial pressure, the degree of the elevation of intracranial pressure is unable to decide accurately with the hemodynamic parameter in the injured dogs. RI and PI increase evidently in part of the injured dogs, suggesting that intracranial pressure is elevated to some extent while arterial perssure lowers markedly again,thus causing brain fusion pressure to lower than some threshold values. The occurrence of this phenomenon may be of potential clinical significance.