Objective: To study the effect of controlled hypotention on the prevention and treatment of cerebral swellingafter removal of giant arteriovenous malformation(AVM). Methods:8 cases with AVM( > 6cm) were selected. When Laser-Dopple flowmetry showed an increase of cerebral blood flow after excision arteriovenous malformation (AVM), intraoperativ-ely, 2.5 % thiopental 5-10mg/kg was injected. Results: The basic mean blood pressure of all cases was 77.63 + 4.27mmHgand basic cerebral blood flow value was 35-134PU. After AVM resection, cerebral blood flow was increased obviously. Thechange value 1 was 125-434PU and the increasing amplitude was 223.48% + 0.62% (P < 0. 001). With thiopental injec-tion, mean artery blood pressure was reduced by 23.00 % + 0.02 %. The cerebral blood flow value was reduced too. Thechange value 2 was 89-236PU and the decreasing amplitude was 35 % + 7.35% (P < 0.01) eampared with that beforethiopental injection. Conclusion:Controlled hypotension can decrease the increasing amplitude of cerebral blood flow and thecerebral perfusion after the giant AVM removal.