Some intracranial aneurysms, such as giant aneurysms, dissecting aneurysms, fusiform aneurysms, etc, were not possible to be treated via surgical or endovascular approaches.Extracranial-intracranial bypass is a procedure that results in the formation of a sizable vascular conduit between the extracranial circulation and the intracranial circulation, which allows the opportunity to sacrifice a major intracranial parent artery.However, when a major parent vessel occlusion was performed, some vessels such as the superficial temporal or occipital artery were not sufficient to revascularise a whole hemisphere.Therefore, how to select a graft vessel becomes a key point to match the blood flow between the graft vessels and recipient vessels in bypass surgery after trapping intracranial aneurysms.