Abstreact objective To explore the effects of dexmedetomidine on cerebral oxygen metabolism and postoperative cognitive function during cardiopulmoary bypass of CHD surgery. Methods 84 childrens with cardiopulmonary bypass of CHD surgery were randomly divided into observation group and control group(n=42) . 2.5% sevoflurane and dexmedetomidine 0.7 μg• kg-1• h-1 was applied during maintenance of anesthesia, while the 2.5% sevoflurane was applied only in control group. At the time points of before cardiopulmonary bypass (T1), when the ascending aorta was open(T2), after cardiopulmonary bypass(T3) and 6 hours after operation (T4) blood from radial artery and right jugular bulb was harvested for blood gas analysis. The jugularn venous oxygensaturation(SjvO2), arterial venous oxygen contentdifference, (Da-jvO2) and cerebral extraction of oxygen (CERO2) were calculated according blood gas analysis, and mini-mental state examination( MMSE) score were evaluated before and 4 day, 3 month and 1 year after surgery. Results The SjvO2 of T2 was higher, but Da-jvO2 and CERO2 was lower than T1, and the differences were statistically significant(P<0.05). The SjvO2 in observation group was higher, but Da-jvO2 and CERO2 were lower than those in control group at T2, and the differences were statistically significant(P<0.05). There were no significant difference in SjvO2 ､Da-jvO2､CERO2 at T3, T4 between two group(P>0.05). There were no significant difference in preoperative MMSE scores between two group(P>0.05). The MMSE scores in observation group at 4 day and 3 month after surgery were (26.53 + 1.54), (27.56 + 1.62), which was significantly higher than that in the control group (24.34 + 1.26) and (25.76 + 1.47), and the differences were statistically significant(P<0.05). But there were no significant difference in MMSE scores at 1 year after surgery between two group(P>0.05). Conclusion Dexmedetomidine could improve cerebral oxygen metabolism and postoperative cognitive function during cardiopulmonary bypass of CHD surgery.