Objectives : This study was designed to investigate the effects of acupuncturing $PC_8$ used perpendicular needling method determine the mechanism of action of acupuncturing $PC_8$ by measuring the changes of regional cerebral blood flow (rCBF) and mean arterial blood pressure (MABP) in normal rats. Methods : This study also investigated the effects of acupuncturing $PC_8$ on the change of rCBF in cerebral ischemic rats, and revealed the mechanism of its action. In addition, the effects of acupuncturing $PC_8$ on focal ischemic brain injury was studied in cerebral ischemic rats. Results : 1. Acupuncturing $PC_8$ significantly increase rCBF but decreased MABP in normal rats. 2. Acupuncturing $PC_8$ increased of rCBF was significantly inhibited by pretreatment with indomethacin (1mg/kg, i.p.), an inhibitor of cyclooxygenase in normal rats. 3. Acupuncturing $PC_8$ increased of rCBF was significantly inhibited by pretreatment methylene blue (10 ${mu}g$/kg, i.p.), an inhibitor of guanylate cyclase in normal rats. 4. Acupuncturing $PC_8$ was significantly improved the rCBF than control group increased unstable in cerebral ischemic rats. 5. Acupuncturing $PC_8$ was not significantly improved the rCBF than control group by pretreatment with indomethacin (1mg/kg, i.p.), an inhibitor of cyclooxygenase in cerebral ischemic rats. 6. Acupuncturing $PC_8$ was significantly increased the rCBF than control group by pretreatment methylene blue ($10{mu}g$/kg, i.p.), an inhibitor of guanylate cyclase in cerebral ischemic rats. Conclusions : In conclusion, our study suggested that acupuncturing $PC_8$ can increase rCBF in normal state, and improve stability of rCBF in ischemic state. In addition, we suggested that mechanisms related with acupuncturing $PC_8$ was involved in the guanylate cyclase pathway.