Obvious swelling of one side of the lower limbs in the elderly is often caused by deep vein thrombosis of the lower limbs, especially in patients who have been bedridden for a long time, and lack of activity, which tends to slow down the blood flow and is the main cause of thrombosis. Patients may present with localized swelling and obvious pain, and in severe cases, tension blisters and even oozing. Ultrasonography can clarify the diagnosis and reveal incomplete deep venous lumen with hypoechoic changes. After diagnosis, anticoagulation should be chosen actively, because lower extremity venous thrombosis is prone to embolus dislodgement, and induce the occurrence of pulmonary embolism, which is serious and life-threatening. During the treatment period, the affected limbs should be elevated to promote venous blood return, and after the condition is stabilized or subacute, the patient can be allowed to leave the bed and wear compression stockings to assist the treatment.