Ｏｂｊｅｃｔｉｖｅ　To observe the regulatory effect of hydrogen on oxidative stress and inflammatory reaction in blood of patients with cardiopulmonary bypass (CPB) grafting under extracorporeal circulation, and to provide a new way for myocardial protection during extracorporeal circulation.　Methods　Thirty patients undergoing CPB grafting under elective general anesthesia were randomly divided into the hydrogen group (n=15) and the control group (n=15). Hydrogen group, 2% hydrogen combined with oxygen was given at the beginning of extracorporeal circulation for 1 h, while oxygen was given to the control group. Radial artery blood samples were collected just before the beginning of skin incision (T0), 5 min after CPB (T1), the end of CPB (T2), 4 h after surgery (T3), and 24 h after surgery (T4) to determine the activity of superoxide dismutase (SOD) and the level of malonaldehyde (MDA), interleukin (IL)-6 and high mobility group box-1 protein (HMGB1) in plasma. Intraoperative hemodynamic indexes［heart rate , central venous pressure (CVP), mean arterial pressure (MAP)］ were monitored and blood gas analysis was performed.　Results　There was no significant difference in plasma MDA level between the two groups at T0 (P>0.05), but plasma MDA levels at T1-T3 in the hydrogen group were significantly lower than those levels in the control group (P<0.05). Similarly, there was no significant difference in plasma SOD activity at T0 between the two groups (P>0.05), but the SOD activities at T1-T3 in the hydrogen group were significantly higher than those activities in the control group (P<0.05). The plasma levels of the inflammatory factors IL-6(T1-T3) and HMGB1(T1-T4) in the hydrogen group were lower than those in the control group(P<0.05). At the same time, the application of 2% hydrogen in extracorporeal circulation had no significant effect on the stability of oxygen and hemodynamics.　Conclusions Hydrogen can reduce oxidative stress and inflammatory reaction in patients undergoing CPB grafting under external circulation, providing a method for myocardial protection during extracorporeal circulation.