Objective To explore the mechanism of Buyang Huanwu Decoction (BYHWD) in reducing oxidative stress levels to protect the blood-brain barrier (BBB) in cerebral ischemia/reperfusion injury (CIRI) rats. Methods: Middle cerebral artery occlusion / reperfusion （MCAO/R）model was established by wire embolization method in rats, and PeriCam PSI laser speckle flow imaging system was applied to detect whether the model establishment was successful. The neurological deficits of rats were evaluated by Zea longa score; The histopathological changes in the rat brain were observed by HE staining; The degree of brain edema was detected by dry and wet weight method; The BBB permeability was detected by Evansblue (EB) staining; Ultrastructural changes of BBB were observed by transmission electron microscopy; The levels of ROS, MDA, and SOD activities, which are related to oxidative stress, were detected by kits; The expression levels of MMP-9 were detected by immunohistochemical staining and Western blot; The protein expression levels of Occludin, ZO-1, and Claudin-5 in TJP were determined by double staining of immunofluorescence and Western blot. Results:BYHWD can reduce neurological deficit scores, alleviate the brain histopathological damage, alleviate the disruption of blood-brain barrier structure, prolonged the dense region of tight junction structure, attenuated the edema of the brain in the ischemic side, and reduce the BBB permeability in MCAO / R rats. BYHWD can decrease the levels of ROS and MDA, increase the activity of SOD, decrease the expression levels of matrix metalloproteinase-9 （MMP-9）, and increase the protein expression levels of Occludin, Claudin-5, and ZO-1. Conclusions: BYHWD can increase BBB tight junction protein expression levels, reduce the permeability of the BBB, protect the ultrastructure of the BBB, and reduce brain edema, and its mechanism may be related to the antioxidant stress of BYHWD and inhibition of MMP-9 activation.