There are three elements of thrombosis: slow blood flow, vascular endothelial cell damage, and a hypercoagulable state of the blood, any of which can promote thrombosis. After major surgery, at least two factors are present: hypercoagulation of the blood due to surgical trauma, bleeding, and active coagulation mechanisms; and bed rest, which slows venous return to the lower extremities. If lower limb deep vein thrombosis is formed, there is swelling and pain in the limb, and in serious cases, the limb ischemic necrosis, which is a local problem. The venous thrombus can also fall off from the place of formation, return to the heart along the blood flow, and then enter the pulmonary artery, stuck in the branch of the pulmonary artery, there is acute pulmonary embolism, the condition depends on the size of the thrombus, the lighter one has chest pain and cough, the heavier one dies suddenly, there is not even time for resuscitation, so it should be prevented. Methods: The simplest, massage the muscles of the lower limbs, from bottom to top, passively, actively move the joints of the lower limbs including ankle, knee and hip; if it does not affect walking, you should get down to the ground early; if there is no active bleeding at the surgical site, you can apply anticoagulant drugs, now generally use low molecular heparin, which is safer.