Chronic intracranial arterial occlusion is something we should pay attention to, because about 10% of all cerebral infarctions are caused by intracranial vascular occlusion, and it can also lead to an annual risk of recurrence of cerebral infarction of 3.6 to 22%. Its etiology is most commonly atherosclerotic, while others can be seen in cardiogenic embolism, vascular entrapment, and arterial inflammation. The mechanism is chronic intracranial arterial occlusion followed by low hemodynamic changes. To recognize this type of disease first we need to know how chronic occlusion of intracranial arteries is diagnosed: it is mainly based on clinical manifestations and neuroimaging. DSA whole brain angiography is still the gold standard for the diagnosis of intracranial arterial occlusion, with good temporal and spatial resolution, allowing dynamic observation of the site, morphology and collateral compensation of the occluded intracranial artery and guiding further treatment strategies. Intracranial arterial occlusion should be evaluated for cerebral collateral circulation: Cerebral collateral circulation refers to when the blood supplying arteries to the brain are severely narrowed or occluded, blood flow reaches the ischemic area through other vessels (collateral branches or newly formed vascular anastomoses), thus allowing different degrees of perfusion compensation to the ischemic tissue. Several studies have suggested the importance of collateral circulation especially for the interventional treatment of acute cerebral macrovascular occlusions. Current opinions on the best lesion assessment: 1) the diagnosis of chronic intracranial arterial occlusion should be actively carried out; 2) cranial CTA/MRA is a noninvasive means of screening for nonacute intracranial large artery occlusion, with high spatial resolution but low temporal resolution; 3) DSA is the gold standard for the diagnosis of chronic intracranial arterial occlusion, with high temporal and spatial resolution; 4) the assessment of chronic intracranial large arterial occlusion should 4) The evaluation of chronic intracranial arterial occlusion should include anatomical assessment of the occlusion site, morphology of the occluded end, length of the occlusion, and the vascular bed distal to the occlusion; 5) Functional assessment of intracranial arterial occlusion should also be performed, such as perfusion assessment and semidark zone assessment, and only those patients with chronic intracranial arterial occlusion who have salvageable brain tissue may benefit from vascular opening therapy; 6) Some emerging imaging techniques (such as HR-MRI) are useful for the diagnosis of chronic intracranial artery occlusion and further opening treatment. Current best treatment advice: 1. Drug therapy remains the basic treatment measure; in patients with symptomatic chronic intracranial artery occlusion who have worsening or recurrent symptoms despite intensive medical therapy, perfusion assessment and collateral circulation assessment reveal that the patient is decompensated, it may be beneficial to carry out intracranial and extracranial artery bypass therapy. However, this is still an invasive treatment with high perioperative risk, and the procedure should be performed in experienced centers. 2. In patients with symptomatic chronic intracranial large artery occlusion who continue to have worsening symptoms or recurrent symptoms after intensive medical therapy, and who are found to have decompensation on perfusion assessment and collateral circulation assessment, endovascular interventional opening therapy may be a safe and effective approach. This is a minimally invasive treatment, but still carries some risk of perioperative complications. Prognosis of chronic intracranial artery occlusion: 1. Chronic intracranial artery occlusion is an important factor in stroke recurrence and poor prognosis. Therefore, the diagnosis and treatment of non-acute intracranial large artery occlusions should be strengthened. 2. The most common sites of non-acute intracranial large artery occlusions are the middle cerebral artery and the intracranial segment of the internal carotid artery in the anterior circulation and the basilar artery in the posterior circulation, and the most common etiology is atherosclerotic; 3. The main mechanism of non-acute intracranial large artery occlusion leading to stroke recurrence is hypoperfusion of cerebral blood flow distal to the occlusion, therefore, treatment aimed at Therefore, therapeutic measures aimed at improving hypoperfusion can help reduce the recurrence of stroke and disability in patients with non-acute intracranial large artery occlusion. In conclusion, chronic intracranial large artery occlusion is common in patients with ischemic infarction/ischemic attacks and is an important risk factor for high recurrence of stroke and poor prognosis. Endovascular treatment has been developed in recent years and may be an effective treatment modality for opening chronic intracranial large artery occlusions because of its minimally invasive nature. However, there is still a lack of unified norms and standards for the indications for vascular interventional opening treatment, timing of opening, opening devices and opening techniques.