Abstract: Objective To discuss the value of transcranial Doppler (TCD) combined with P_ETCO₂ in the evaluation of cerebrovascular reserve in patients with cerebrovascular stenosis. Methods Total 78 patients with cerebrovascular stenosis were divided into single vascular stenosis group (32 cases) and multiple vascular stenosis group (46 cases), and 45 normal health patients were assigned into the control group. TCD combined with P_ETCO₂ were used to evaluate the cerebrovascular reserve function. Results There was no statistically significant difference in the vasodilation reserve and the total blood vessel reserve among the three groups (both the light side and the heavy side), all P>0.05. The systolic reserve of vasorelaxation in serious side was significantly lower in the multivessel stenosis group than that in the control group (t=2.417, P<0.05). The vascular dilation reserve value and vascularity in the single vessel stenosis group were obviously lower than those in the multi-vessel stenosis group (all P<0.05). There was no significant difference in the P_ETCO₂ during terms of quiet breathing, hypocapnia, and hypercapnia among the three groups (all P>0.05). The severity of cerebral vascular disease was negatively correlated to the vascular expansion reserve value and the overall blood vessel reserve value (all P<0.05), and no correlation with vascular contraction reserve (P>0.05). Conclusion TCD combined with P_ETCO₂ is a kind of effective method to evaluate cerebrovascular reserve function. With the increase of severity of cerebral vascular stenosis, cerebral vascular reserve might significantly decrease, which will result in the alteration of risk of stroke.