Background　The cardiopulmonary bypass brings about complex pathophysiological changes， especially blood coagulation disorders. Prolonged blood contacting with the artificial surface of the cardiopulmonary bypass circuit， severe hemodilution， high doses of heparin and hypothermia are all possible triggers of a coagulopathy which leads to excessive bleeding. Sometimes it might need surgical re-interventions.　Objective　To protect the coagulation function of patients undergoing cardiopulmonary bypass surgery is to reduce bleeding and blood transfusion.　Content　The literature about the pathophysiological changes and preventive measures of coagulopathy in patients undergoing open heart surgery with cardiopulmonary bypass in past ten years are discussed and updated in this review.　Trend　We should use a multi-modal approach to reduce the impact of CPB on coagulation function and correct coagulant dysfunction timely.