Platelets can secrete 5-hydroxytryptamine and catecholamines, antifibrinolytic factor, platelet factor and other substances. 1. 5-hydroxytryptamine and catecholamines: the hemostatic effect of platelets is due to the release of vasoconstrictor substances, such as 5-hydroxytryptamine and catecholamines to make the injured blood vessels constricted in order to reduce the outflow of blood, together with the platelets aggregated into a cluster to block the damaged blood vessels, so as to achieve the purpose of coagulation and hemostasis. 2. Anti-fibrinolytic factor: inhibit the cleavage activity of fibrinolytic system, so that the formed clot is not easy to disintegrate, thus achieving the effect of coagulation. 3. Platelet factor: such as platelet factor 3, which is one of the phospholipid components of platelet membrane and an important factor involved in platelet coagulation. Under the combined effect of the above substances, the process of coagulation can be completed.