Previous studies suggest that it may be inappropriate to determine treatment strategies solely based on the degree of stenosis for patients with intracranial atherosclerotic stenosis (ICAS). In order to better risk stratify patients with ICAS, we developed a novel non-invasive fractional flow (FF) calculation technique based on intracranial angiography (Angio-FF) to assess the hemodynamics for patients with ICAS. This study aims to investigate the difference in FF between symptomatic and asymptomatic patients with ICAS and its potential optimal threshold.