Objective To investigate the effect of different doses of protamine neutralizing heparin on perioperation of on-pump coronary artery bypass graftting (CABG).Methods A total of 180 on-pump CABG patients hospitalized from January 2015 to November 2016 were randomly divided into three groups,the protamine group l,protamine group 2 and protamine group 3,60 patients in each group.Heparin (3 mg/kg) was used before extracorporeal circulation.After intracardiac operation was over,protamine was used to neutralize the heparin to adjust the activated clotting time (ACT) in protamine group 1,which was 10％ higher than that of intubation.Meanwhile,protamine group 2 was neutralized to equal to the ACT before intubation,and protamine group 3 was 10％ lower than that before the intubation.The differences of intraoperative and postoperative parameters were compared between the three groups.Results No death was found in the three groups during hospitalization.Comparing with protamine group 1 and protamine group 2,the time of operation,the ACT before the leaving operation room,the ACT of the first hour after returning to ICU,the amount of bleeding during operation,the time of closing and the amount of red blood for transfusion were decreased in protamine group 3 (P ＞ 0.05).The total amount of protamine for neutralizing and the ratio of protamine and heparin were significantly increased in protamine group 3 (P ＜ 0.05).The heart dysfunction after operation,perioperative myocardial infarction,pulmonary edema,pulmonary infection,renal dysfunction,poor wound healing,neurological complications,and time of in hospital stay showed no significant differences between three groups (P＞0.05).Conclusion ACT below 10％ of preoperation is safe,after neutralization of heparin by protamine,which can obviously reduce the bleeding,the time of sternal closure and the amount of red blood cell transfusion,showing a positive clinical significance.