Abstract: Objective To investigate the feasibility of carotid artery ultrasound in evaluating severe stenosis or occlusion in vertebral artery (VA).Methods A total of 205 patients with severe stenosis or occlusion in unilateral VA intracranial segments who were admitted to the Affiliated Huai'an Hospital of Xuzhou Medical University from January 2019 to December 2022 were enrolled as a research group. Among them, 35 cases had no diastolic blood flow signal, so the other 170 cases in the research group were selected for statistical analysis. According to the diameter of the vertebral artery intervertebral segment, the patients were further divided into two groups:a group with thin diameter in the intervertebral segment (n=90) and a group with normal diameter (n=80). Meanwhile, another 90 patients with one vertebral artery physiologically thin without stenosis, and 80 patients with normal diameter without stenosis in both vertebral arteries who were admitted to the Affiliated Huai'an Hospital of Xuzhou Medical University were included as a control group. Color Doppler ultrasonography (CDU) was performed in all the patients. Their diameter (D), peak systolic velocity (PSV), end diastolic velocity (EDV), and resistance index (RI) of the bilateral vertebral and internal carotid arteries in the research and control groups were recorded, and the differences in parameters between the bilateral vertebral and internal carotid arteries were calculated. Using the results of CT angiography (CTA) and Digital subtraction angiography (DSA) as the gold standards, ROC curves were plotted to analyze the feasibility of the hemodynamic parameters of the extracranial segment of the vertebral artery to evaluate the severity of stenosis or occlusion of the intracranial segment.Results Compared with the control group, the research group showed statistical decreases in PSV and EDV, and increases in RI (P<0.05). For the thin diameter group:vertebral artery RI ≥ 0.74, bilateral vertebral artery RI difference ≥ 0.13, and vertebral artery and internal carotid artery RI difference ≥ 0.15 were the independent predictors of severe stenosis or occlusion of VA intracranial segment. The area under the ROC (AUC) of the three parameters combined was 0.995, and the optimal threshold of the combined factor was 0.674, with a sensitivity of 97.0%, and a specificity of 96.3% (P<0.05). For the normal diameter group, vertebral artery RI ≥ 0.74, EDV ≤ 12.05 cm/s, bilateral vertebral artery RI difference ≥ 0.09, EDV difference ≥ 5.0 cm/s, and vertebral artery to internal carotid artery RI difference ≥ 0.10, were the independent predictive factors for severe stenosis or occlusion of VA intracranial segment. The AUC of the ROC of the combined five parameters was 0.992, and the optimal threshold of the combined factors was 0.631, with a sensitivity of 96.4% and a specificity of 95.6% (P<0.05).Conclusions Carotid artery ultrasound can effectively evaluate severe intracranial stenosis or occlusion of VA.