Antithrombin, abbreviated AT, is the body’s primary anticoagulant. Firstly, it inactivates factor 10 and factor 2 in the body, and accounts for more than 75% of the physiological anticoagulant activity of plasma. Secondly, antithrombin is mainly produced by human liver and endothelial cells of blood vessels, and it can inactivate Factor 9, 11 and 12 in addition to Factor 10 and 2. After the combination of antithrombin and heparin again, the structural changes and exposure of the active center of antithrombin will have a stronger anticoagulant effect. Only when the body’s antithrombin functions properly, the body’s coagulation system, anticoagulation system, and fibrinolytic system can cooperate with each other to maintain the smooth flow of blood as well as to avoid thrombosis and bleeding. Therefore, antithrombin is the main anticoagulant substance in the body, which can prevent thrombosis.