Lower extremity deep vein thrombosis is an abnormal clotting of venous blood in the deep veins of the lower extremities, blocking the venous lumen and resulting in venous return obstruction. This disease can be complicated by pulmonary embolism in the acute stage and affects life and work ability in the later stage due to post-thrombotic syndrome. Venous injury, slow blood flow and hypercoagulable state of blood are the three main factors that cause deep vein thrombosis. Venous injury includes chemical injury, mechanical injury and infectious injury. Slow blood flow is caused by prolonged braking, bed rest due to illness, and sedentary. Hypercoagulable blood is seen in trauma, post-surgery, tumors, long-term use of birth control pills, pregnancy, and postpartum. Symptoms are varied and most patients present with swelling and edema of the lower extremities. In addition, there can be pain in the lower extremities, erythema, fever, superficial venous dilatation, pain in the lower legs when the foot is dorsiflexed, and cyanosis of the swollen lower extremities. Ultrasound Doppler examination, radionuclide examination or lower extremity venous cascade angiography may be performed. When the diagnosis is clear, anticoagulant and depolymerizing drugs can be given. In severe cases, surgical removal of the embolus can be performed. The disease may leave lower limb edema, secondary varicose veins, dermatitis, hyperpigmentation, and stasis ulcers. Deep vein thrombosis of the lower extremities can cause fatal pulmonary embolism, and early diagnosis and treatment must be emphasized.