The concept of “time window” was introduced in the 1990s, and experts have particularly emphasized its relevance to the prognosis of ischemic stroke. Studies have shown that most ischemic strokes begin in the middle cerebral artery. The cause is usually thrombosis based on atherosclerosis, resulting in severe ischemic injury and necrosis of the local tissues, leading to clinical manifestations of neurological deficits, such as hemiparesis, loss of hemianesthesia and ipsilateral hemianopia. In a lesion with middle cerebral artery thrombosis as the core, three regions are often formed, including the central ischemic region, the reversible ischemic injury region and the ischemic hemianopia. The degree of ischemia and the degree of tissue damage vary in each region. In general, the ischemic central zone is small in extent, but the tissue damage is extremely severe, and the ischemia will develop into irreversible brain damage in less than one hour after the occurrence of ischemia, and the neural tissue in the zone will become necrotic. There is a larger area of reversible ischemic injury around the central ischemic area. Although the cells of brain tissue in this area have different degrees of degeneration and corresponding neuroischemic symptoms, there is still a small amount of blood supply in the tissue, so the development is slow. If the blood supply can be restored in 3-6 hours, this reversible ischemic injury zone can be transformed into a subclinical ischemic dark zone, which can reduce and subside the degeneration of brain tissue cells and avoid necrosis. On the contrary, if this area continues to be ischemic for more than 6 hours or longer, the reversible damaged brain tissue will progress to irreversible damage and cause severe degeneration and necrosis of brain tissue cells in the area, thus expanding the infarct foci, making the degree of neurological damage more serious and the patient’s prognosis worse. Therefore, for the treatment of ischemic stroke, the concept of “time window” must be firmly established. That is, from the onset of stroke, we should strive to give thrombolytic drugs within the “time window” of 3 to 6 hours, so as to make the thrombus in the cerebral artery dissolve or become smaller as possible, and increase the blood supply to the infarct area, so that the central ischemic area is reduced or no longer enlarged, and the potentially reversible ischemic area is gradually transformed into an ischemic semi-dark area, so as to achieve the clinical treatment of reducing The aim of clinical treatment is to reduce the injury, promote the recovery of neurological function and reduce the degree of disability in the future, and actively strive for the best prognosis.