Objective To assess cerebrovascular reserve ( CVR) function in patients with internal border zone infarction(IBZI) induced by severe middle cerebral artery (MCA) stenosis, and investigate the impact on progression and outcome of the disease .Methods A total of 84 patients with unilateral severe MCA stenosis were selected . Hypercapnia was induced by holding breath .The change of blood flow velocity in MCA was measured by transcranial Doppler ( TCD ) to calculate CVR .According to CVR , patients were divided into impaired regional CVR group ( CVR <10%) and normal CVR group ( CVR ≥10%) .The NIHSS was used to evaluate neurological function in both groups within 14 d, and mRS was used to evaluate acute stage outcome of the patients at discharge .All the patients were followed-up for 6 months, the incidences of recurrence , complications and mortality in the two groups were analyzed .Results The incidence of progressive cerebral infarction in the impaired regional CVR group (67.39%) was significantly higher than that in the normal CVR group (42.11%) ( P<0.05).The impaired regional CVR group showed higher proportion of patients with poor clinical outcome at discharge ( mRS≥3 ) (63.04%)compared to the normal CVR group (36.84%) (P<0.05).In the followed-up 6 months, the incidences of recurrence and complications were 34.78% and 45.65% respectively in the impaired regional CVR group , they were significantly higher than that in normal CVR group (15.79%,23.68%)(P<0.05).The overall mortality rates did not differ significantly between the two groups ( P>0.05 ) .Conclusion Impaired regional CVR may be predictive of subsequent progressive cerebral infarction and poor clinical outcomes in patients with IBZI induced by severe MCA stenosis .