Objective To investigate the correlation of regional leptomeningeal score （rLMC） based on multi-mode CT with infarct volume and hemorrhage transformation in acute ischemic stroke and its application value in clinical practice.Methods A retrospective analysis was performed for the patients with acute occlusive ischemic stroke of large artery who experienced first disease onset for ≤6 hours and were admitted to our hospital from October 2019 to October 2020. After hemorrhagic lesion was excluded by cranial CT scanning， the lesions were divided anterior cerebral artery （ACA）-middle cerebral artery （MCA） region and posterior cerebral artery （PCA）-MCA region based on rLMC assessment. Six subscales were used for leptomeningeal artery classification， and computed tomographic angiography （CTA） collateral score was the total score of the 2 regions （1-10 points）. Within 3 days after admission， DWI sequence was performed in addition to conventional cranial MR sequence to determine infarct volume and the presence or absence of hemorrhage transformation. Routine CT reexamination was performed on days 10-14 after admission or at the time of aggravation to observe the presence or absence of hemorrhage transformation.Results There were significant differences between different rLMC groups in family history of stroke， history of coronary heart disease， NIHSS score on admission， and fasting blood glucose （P<0.05）. Meanwhile， rLMC score was negatively correlated with cerebral infarct volume （γ=-0.735， P<0.001）. There were significant differences between different rLMC groups in infarct volume and incidence rates of symptomatic intracranial hemorrhage and post-interventional cerebral hyperdensities （P<0.05）. The multivariate logistic regression analysis showed that family history of stroke， blood glucose， and NIHSS score on admission were influencing factors for leptomeningeal collateral circulation.Conclusions rLMC is negatively correlated with infarct volume and hemorrhagic transformation in acute ischemic stroke and can effectively reflect the progression and severity of acute ischemic stroke.