Leech is a Chinese herbal medicine with the function of activating blood circulation, dispersing blood stasis and promoting menstruation, which is mainly used to treat diseases caused by blood stasis. And leechin is an extract from the salivary gland of leech, and modern pharmacological research shows that leechin has certain therapeutic effects against thrombosis and can also be helpful in inhibiting thrombosis. The formation of thrombus is mainly caused by a series of complex changes caused by the hydrolysis of protein by thrombin, which eventually causes clotting and leads to the formation of thrombus. While hirudin can bind to thrombin and thus can prevent the formation and development of thrombus, hirudin is also used as one of the effective drug ingredients for the treatment of disseminated intravascular coagulopathy. Because of its anticoagulant and antithrombotic effects, hirudin is widely used in the treatment of venous thrombosis, cerebral thrombosis, and other diseases where thrombosis exists. Although hirudin has a strong stability of its own structure and can easily bind to thrombin molecules, hirudin still has some side effects, such as slight bleeding in patients with long-term heavy use, and also allergy in a small number of patients. Therefore, it is recommended to use it in combination with traditional anticoagulant drugs such as heparin and aspirin, and also note that it is prohibited for weak people, pregnant women and menstruating women.