Objective  To investigate the effect of calycosin on cerebral ischemia/reperfusion injury and its mechanism.    Methods  Forty SPF male SD rats were randomly divided into sham group, model group, calycosin group (20 mg/kg), nimodipine group (0.7 mg/kg, positive control group). The occlusion model of middle cerebral artery in rats was established by modified thread occlusion method,and the environment of cerebral ischemiareperfusion injury was simulated in vivo. Zea longa score was used to detect the neurological deficit of rats after ischemiareperfusion injury, 2,3,5-triphenyltetranitrogen (TTC) was used to detect the volume of cerebral infarction, HE staining was used to detect the pathomorphological changes of nerve cells, Nissl staining was used to observe the changes of nissl bodies, TUNEL staining was used to detect the apoptosis of nerve cells, Western blotting was used to detect the expression of cytochrome C (Cyt C), apoptotic protease activating factor-1 (Apaf-1), Caspase-9 and Caspase-3.    Results  Compared with the sham group, the neurological deficit symptoms in the model group were significant (P<0.05), the volume of cerebral infarction increased significantly (P<0.05). Under the microscope, it was found that the nerve cells showed contraction of cell body, hyperchromatic and pyknosis of nucleus and poor growth state, the expression of nissl body reduced significantly (P<0.05), the apoptotic nerve increased significantly (P<0.05), the expression of Cyt C, Apaf-1, Caspase-9 and Caspase-3 increased significantly (P<0.05).Compared with the model group, the neurological deficit symptoms of calycosin group and nimodipine group reduced significantly (P<0.05), the volume of cerebral infarction reduced significantly (P<0.05). Under the microscope, the damage of nerve cells reduced significantly , the expression of nissl body increased significantly (P<0.05), the apoptotic nerve reduced significantly (P<0.05), the expression of Cyt C, Apaf-1, Caspase-9 and Caspase-3 decreased significantly (P<0.05)   Conclusion  Calycosin can significantly inhibit the apoptosis of nerve cells and reduce the cerebral ischemia-reperfusion injury. Its mechanism of action is related to the effective regulation of Cyt C/Apaf-1 apoptosis signaling pathway by calycosin.