Abstract: Objective: In order to explore the variability of anesthetic depth in hemorrhagic patients and its mechanism, the study investigated how MAC and β-endorphin changed in state of hemorrhagic hypotension. Methods: ① 20 New Zealand rabbits were randomly divided into control group and hemorrhage group. MAP、CVP、P ET CO 2 and ECG were monitored continuously. ② The MAC of sevoflurane was measured in the two groups in which MAP of hemorrhage group was dropped to two third of baseline by bloodletting. ③ Plasma β-endrophin concentration was assaied repeatedly in two groups. Results: ① MAC of sevoflurane was （2.2±0.2）% in control group and （1.6±0.1）% in hemorrhage group. ② Hemorrhage induced increase of plasma β-endorphin concentration significantly. 5 min and 30 min after bloodletting, β-endorphin concentration increased （50±9）% and （58±10）%, respectively. Conclusion: MAC of sevoflurane in rabbits is （2. 2±0.2）%. Acute hemorrhage could induce endogenous β-endorphin releasing enormously, which maybe one of the mechanisms to reduce MAC of inhalational anesthetic.