Objective To determine the clinical effect and significance of transcranial Doppler (TCD) in the early warning of delayed cerebral ischemia (DCI) induced by aneurysmal subarachnoid hemorrhage (aSAH).Methods Eighty-five aSAH patients, who were dynamically and continuously monitored with TCD, were divided into two groups after clinical diagnosis:DCI group and non-DCI group, which were analyzed and compared in terms of their mean cerebral blood flow velocity (MBF) in the middle cerebral artery (MCA), pulsatility index (PI), and prognosis.Results Thirty patients (35.3%) in all the 85 patients were diagnosed with DCI, and 56.7% of these cases occurred within 6~8 days of onset. After admission, MBF in the DCI group significantly increased from their initial MBF result (t=23.847, P=0.000), but PI in the DCI group (t=0.733, P=0.468), MBF in the non-DCI group (t=0.547, P=0.585), and PI in the non-DCI group (t=0.573, P=0.568) were not significantly changed. The DCI group had a significantly lower proportion of patients with good Glasgow Outcome Scale scores than the non-DCI group (χ²=11.5145, P=0.001). The moderate disability rate and vegetative survival rate in the DCI group were significantly higher than those in non-DCI group (χ²=4.1098, P=0.043, P=0.041). There were no significant differences in mortality rate and severe disability rate between the two groups (P=0.122 and 0.339).Conclusions TCD, due to its advantages of non-invasiveness and continuous monitoring, may become an effective method for the early warning of DCI induced by aSAH, thus providing guidance for clinical intervention.