Abstract: Objective The hemodynamic changes of middle cerebral artery (MCA) and superficial temporal artery (STA) during superficial temporal artery-middle cerebral artery (STA-MCA) bypass were observed by transcranial Doppler ultrasound (TCD) - 16M ultrahigh frequency probe. Methods From June 2015 to January 2019, 31 patients with moyamoya disease whose internal carotid artery (ICA) occlusion or MCA trunk occlusion affected distal MCA blood supply disorder were retrospectively included by DSA or CTA,STA-MCA bypass was performed, TCD-16M probe was used to monitor the changes of MCA blood flow before and after bypass and STA blood flow after bypass, so as to judge the patency of anastomotic stoma and bypass vessels. Results The blood flow spectrum of 31 patients showed low flow and low resistance before operation, and the blood flow spectrum of STA was "high resistance". After MCA-STA bypass, the blood flow velocity of distal and proximal segments of MCA increased significantly (P<0.05), and the resistance index (RI) increased slightly, but there was no significant difference between the two groups (P>0.05). The blood flow velocity of STA increased significantly after MCA-STA bypass, while the RI decreased (P<0.05). Conclusions TCD can effectively monitor the changes of MCA and STA blood flow in real time during operation, and provide favorable evidence for judging the patency of anastomotic and bypass vessels.