Objective To demonstrate the carotid artery hemodynamic characteristics in patients with common carotid artery occlusion,and to investigate the value of color Doppler ultrasonography in evaluating it.Methods 30 patients with common carotid artery (CCA) occlusion or severe stenosis (stenosis rate＞70％) were as the patients group,while 30 volunteers with the normal indicators of carotid artery ultrasonography as the control group.In both groups,the examinations of the CCA,the internal carotid artery (ICA),the external carotid artery (ECA) and the vertebral artery (VA) were taken by color Doppler ultrasonography under quiescent conditions.Bilateral carotid ultrasonography studies were performed,which included the peak systolic velocity (PSV),end-diastolic velocity (EDV),mean velocity (MV),and resistance index (RI).Results The peak systolic velocity (PSV),EDV and MV of ICA were obviously lower in case group at affected side than in the control group (P＜0.05 or 0.01).The blood flow of ECA at the affected side was retrograde or bidirectional.PSV,EDV and MV of the external carotid artery (ECA) were obviously higher in the healthy side in patients than in the control group (all P＜0.01).There was a significant difference in blood flow velocity of bilateral vertebral artery (VA) between the patients group and the control group,and the PSV,EDV and MV were obviously higher in the former than in the latter (all P＜0.01).And the RI was different between the two groups (P＜0.05).Conclusions The pressure of ICA is dropped after the common carotid artery occlusion,and then ECA reversely feeds ICA by collateral circulation.The blood flow velocities of bilateral vertebral artery and contralateral ECA are significantly increased to compensate for cerebral blood supply through collateral circulation channels.Color Doppler ultrasonography can reflect this phenomenon more fully and accurately,and provide clinically valuable diagnostic information.