Swelling of the lower extremities in the elderly is caused by the formation of deep vein thrombosis in the lower extremities. After the formation of deep vein thrombosis in the lower extremities, the venous blood flow is obstructed, which causes stagnation of venous blood and increases venous pressure, so that the blood in the veins penetrates through the vessel walls into the subcutaneous tissues, resulting in increased tissue fluid in the lower extremities of the body and causing swelling of the lower extremities. At the beginning, the tension of the skin is increased, and it is difficult to appear finger sink edema when pressing. As the disease prolongs and the thrombosis is mechanized, finger sink edema will appear in the lower limbs, especially when moving, and the swelling of the lower limbs will be aggravated, and the swelling of the lower limbs will be reduced by raising the limbs. Due to the formation of deep vein thrombosis in the lower limbs, the thrombus may dislodge in the acute stage and cause pulmonary embolism, and then the patient’s life will be endangered.