LMWH in medicine refers to low molecular heparin, which is a kind of heparin fragment with lower molecular weight obtained by chemical decomposition or enzyme-catalyzed cleavage of common heparin. Its characteristics are strong antithrombotic function, few side effects, and no laboratory testing.1.Mechanism: the main mechanism of action of low molecular heparin is to exert anticoagulant effect by binding antithrombin, and can inhibit a variety of thrombin, which is an antithrombin-dependent thrombin inhibitor.2.Role and Indication: it has the functions of anticoagulation, anti-inflammation, anti-thrombosis, inhibition of glomerular thylakoid cell proliferation, and regulation of maternal immunity. 2. Actions and indications Anticoagulation and antithrombotic effect can inhibit the formation of thrombus and arteriovenous thrombosis in vitro and in vivo, but does not affect the aggregation of platelets, commonly used in coronary heart disease, cerebral infarction, venous thrombosis and other diseases. Anti-inflammatory and inhibit the proliferation of glomerular tethered cells, often used in kidney diseases. The role of regulating maternal immunity, can inhibit the function of natural killer cells, reduce the maternal immune attack on the embryo, for the treatment of embryonic dysplasia, spontaneous abortion, recurrent miscarriage has a certain effect; 3. Contraindications: hypersensitivity to heparin, perinatal women, severe hepatic and renal insufficiency, hemophilia, subacute bacterial endocarditis, visceral tumor patients can not apply low molecular heparin; 4, Adverse reactions: fever, headache, nausea, vomiting, local swelling, urticaria and other symptoms may occur; 5. Precautions: Application of low molecular heparin may easily cause local hematoma, and intramuscular injection is prohibited. The use of low molecular heparin should be in accordance with the indications for the use of the drug and should be used under the close guidance of a physician.