It is a common clinical imaging manifestation that new abnormal high density image appears on brain CT immediately after mechanical thrombectomy in patients with acute cerebral infarction. CT high density imaging usually includes contrast enhancement， contrast extravasation or cerebral hemorrhage， among which cerebral hemorrhage is a more serious complication. It is found that CT high density imaging has certain predictive value on final infarct volume， intracranial hemorrhage transformation and functional prognosis. The presence of high-density CT images often predicts a higher risk of intracranial hemorrhage transformation and poor prognosis （90 d modified Rankin scale ≤ 2 points）. The occurrence mechanism of CT high density shadow is very complex and has not been fully understood. Currently， it is generally believed that the occurrence and development of CT high density shadow is related to the destruction of the blood-brain barrier， the application of anticoagulants， ischemia-reperfusion injury， the injury of vascular wall by interventional instruments， the toxic and side effects of contrast agents and many other factors. It is of great significance to explore the related mechanisms of intracranial hemorrhage to reduce the incidence and improve the prognosis of patients. This paper reviews the research progress on the mechanism of high density imaging after mechanical thrombectomy in patients with acute cerebral infarction.