Objective To observe the effects of Buyang Huanwu Decoction(BHD)on collateral circulation of patients with acute cerebral infarction(ACI)through transcranial Doppler sonography(TCD). Methods The randomized controlled trial methods were applied, and 80 ACI patients were randomly divided into treatment group and control group, 40 cases in each group. Two cases from each group were dropped out, and the left 38 cases of each group were included into the analysis. The control group was treated with the standardized western medicine regimen, and the treatment group was given BHD orally on the basis of treatment for the control group. The treatment for the two groups covered 7 days. On treatment day 3 and 7, TCD was adopted to investigate the blood flow velocity of the responsible vessels and the improvement of collateral circulation compensation. On treatment day 7, the scores of National Institute of Health Stroke Scale(NIHSS) in the two groups were compared. Results (1) On treatment day 3, collateral circulation improvement occurred in 12 patients(accounting for 31.58%)from the treatment group , and on treatment day 7 , the improved cases increased to 16(accounting for 42.11%). In the control group , 3 cases(7 . 89%) were improved on treatment day 3 , and 4(10 . 53%) improved on treatment day 7. The treatment group had better effect on improving collateral circulation than the control group, the difference being significant(P<0.01). (2) In the treatment group, 9 cases had increased blood flow velocity(Vm) of the responsible vessels on treatment day 3, and 11 cases had the increase on treatment day 7. In the control group, Vm increase occurred in one case both on treatment day 3 and 7. The treatment group had better effect on increasing Vm than the control group, the difference being significant(P<0.05). (3) On treatment day 7, NIHSS scores were decreased in both groups(P<0.05 or P<0.01), and the decrease of the treatment group was superior to that of the control group(P<0.01).(4) No adverse event was shown in the two g roups during the treatment. Conclusion BHD can constantly improve the blood flow velocity of the responsible vessel and promote collateral vessel building , which results into the recovery of the impaired neural function.