Old left lower extremity venous thrombosis needs persistent treatment and good life care. Obsolete left lower extremity venous thrombosis mostly refers to the left lower extremity venous thrombosis that has been ill for more than one month. It is characterized by recurrent attacks and requires persistent treatment, or else the old left lower extremity venous thrombosis may develop a new thrombus on top of the existing one. The disease can lead to venous return obstruction in the left lower extremity, and thrombus dislodgement may also cause hemiplegia, pulmonary embolism, and even life-threatening. Old left lower extremity venous thrombosis may be treated with anticoagulant drugs such as rivaroxaban, and in severe cases, surgery may be required. Usually, you should pay attention to rest and avoid swelling of the affected limbs. When sleeping, you can use pillows to elevate the affected limb, and pay attention to keep your body warm. It is recommended that patients with old venous thrombosis of the left lower extremity go to the hospital in time, listen to the doctor’s treatment plan, and regularly review their condition.