Abstract: Objective:To investigate the relationship between the degree of unilateral middle cerebral artery(MCA) stenosis and CT perfusion(CTP) parameters in the first trimester of cerebral infarction, and to analyze the changes of vascular surface permeability(PS) in the first trimester of infarction. Methods:A total of 108 patients with unilateral middle cerebral artery MCA stenosis diagnosed by head and neck CTA from July 1, 2018 to October 1, 2019 in our hospital were retrospectively analyzed. The imaging characteristics of CTP were observed. The peak time(TMax), mean transit time(MTT), cerebral blood flow(CBF), cerebral blood volume(CBV) and surface permeability(PS) of the residual function of the stenotic and mirror sides in each group were measured, and the relative values of each perfusion parameter(stenotic/mirror side) were calculated. The correlation between the degree of unilateral middle cerebral artery stenosis and CT perfusion parameters in the early stage of cerebral infarction was analyzed. Results:(1) 39 of 108 patients with unilateral middle cerebral artery stenosis had abnormal perfusion, and there was significant difference in perfusion stage of different degrees of vascular stenosis(P=0.009). The degree of unilateral middle cerebral artery stenosis was moderately positively correlated with the stage of abnormal perfusion(r=0.557, P=0.000);(2) There were significant differences in rCBF value and r MTT value of different degrees of unilateral middle cerebral artery stenosis(P<0.05), but there was no significant difference in rCBV value and rTMax value(P>0.05). The degree of unilateral middle cerebral artery stenosis was positively correlated with rTMax values and rMTT values(r=0.458, P=0.003, r=0.765, P=0.000, respectively), negatively correlated with rCBF(r=-0.600, P=0.000), and there was no significant correlation between the degree of stenosis and rCBV values;(3) There was a significant difference in the absolute value of PS between the awn and mirror side in patients with stages IIa and IIb(P<0.05), and there was no significant difference in the relative value of PS between patients with stages IIa and IIb(P>0.05). Conclusion:The degree of unilateral MCA stenosis is related to the degree of unilateral middle cerebral artery stenosis in patients with certain correlation between the degree of unilateral MCA stenosis and the stage of early cerebral infarction. Unilateral TMax is the most sensitive indicator for evaluating the abnormal cerebral perfusion. The more severe the degree of MCA stenosis, the greater the rTMax and rMTT values, the smaller the rCBF; there is a change of increased vascular surface permeability in stage II of early cerebral infarction.