Under normal conditions, blood flows smoothly in the blood vessels, neither bleeding nor thrombosis, mainly by two factors: on the one hand, the inner surface of the blood vessels covered with a layer of endothelial cells, endothelial cells have an endocrine function, the secretion of substances can regulate the coagulation, anticoagulation and fibrinolytic system; on the other hand, depends on the coagulation, anticoagulation and fibrinolytic system in the body of the two systems of the inter-balance, mutual constraints. The coagulation system and the anticoagulation and fibrinolytic systems. The coagulation system and the anticoagulation system (fibrinolytic system) antagonize each other. Under physiological conditions, the coagulation factors in the blood are constantly activated, resulting in the production of thrombin and the formation of microfibrin, which is deposited on the endothelium of the blood vessels. However, these microfibrin is constantly dissolved by the activated fibrinolytic system, and at the same time, the activated coagulation factors are constantly phagocytosed by mononuclear phagocyte system. The dynamic balance between the coagulation and fibrinolytic systems described above ensures that the blood is both potentially coagulable and fluid. However, sometimes the above dynamic balance is disrupted by the action of certain factors that can promote the coagulation process, triggering the coagulation process, and the blood can then coagulate in the cardiovascular cavity and form a thrombus. For example, once a small blood clot appears in the body, the anticoagulant system is activated to prevent further expansion of the clot, and at the same time, the fibrinolytic system is active and can dissolve the small clot. And once a blood vessel ruptures and blood flows out of the vessel, the coagulation system is immediately activated to form a thrombus to plug the rupture site and stop the blood from spilling out into the vessel. However, when the body’s systemic or local coagulation system is strengthened or the anticoagulation system is weakened, and the ability of the fibrinolytic system (thrombolysis) is decreased or the antifibrinolytic properties are enhanced, the formation of a thrombus or the formation of a thrombus that is not able to be cleared out of the body can occur under the action of certain triggers.