OBJECTIVE： To screen the best proportion of Astragalus membranaceus injection combined with Erigeron breviscapus injection against cerebral ischemia-reperfusion injury in rats. METHODS： Male SD rats were randomly divided into sham operation group， model group and administration group [different A. membranaceus injection-E. breviscapus injection proportion groups， being A（0 ∶ 10）， B（2 ∶ 8）， C（4 ∶ 6）， D（6 ∶ 4）， E（8 ∶ 2）， F（10 ∶ 0）groups， set by baseline geometric proportion increasing and decreasing design]， with 8 rats in each group. Except for sham operation group， reperfusion injury model of middle cerebral artery occlusion were induced by modified suture method in rats. The each administration group was given relevant medicine intraperitoneally once immediately after inducing model， and then given again after 24 hours （medication interval between the two injections of 30 min）. Constant volume of normal saline was given to rats in sham operation group and model group. Forty-eight hours after reperfusion， Longa scoring method was used to evaluate neurological impairment of rats， and neurological impairment score was recorded. Serum content of MDA and activity of SOD were measured by colorimetry assay. TTC assay was used to detect cerebral infraction， and cerebral infarction rate was calculated. Kim’s formula was used to calculate the synergistic index （q） of rats in administration groups. RESULTS： Compared with sham operation group， neurological impairment score and serum content of MDA were increased significantly in model group， while activity of SOD was decreased significantly （P＜0.01）. The area of cerebral infarction increased significantly， and the rate of cerebral infarction increased significantly （P＜0.01）. Compared with model group， neurological impairment scores and serum contents of MDA were decreased significantly in group A， B， C， D and E； neurological impairment score of group C was significantly lower than those of group A and F； serum contents of MDA in group B， C， D and E were significantly lower than that of group F （P＜0.05 or P＜0.01）. Activities of SOD in group A， B， C， D and E were increased significantly， and group C was significantly higher than group F （P＜0.05 or P＜0.01）. The cerebral infarction area of rats in each administration group was reduced to varying degrees. The cerebral infarction rates of rats in group B， C， D and E were significantly reduced， and group C and D were significantly lower than group F， while group C was significantly lower than group A （P＜0.05 or P＜0.01）. The q values of group B， C， D and E were 0.90， 1.30， 1.00， 0.70 （neurological impairment score） and 0.79， 1.27， 0.98， 0.82 （cerebral infarction rate）. CONCLUSIONS： Different ratios of A. membranaceus injection and E. breviscapus injection have certain protective effects on cerebral ischemia-reperfusion injury model rats， can relieve their neurological deficits， alleviate their oxidative stress and reduce their cerebral infarction areas. The effect of the combination of the two drugs is better than that of single use， and the optimum ratio is 4 ∶ 6.