After a venous thrombosis of the lower extremity blocks a blood vessel, the thrombosed limb becomes severely swollen, so measuring the circumference of the leg after a thrombosis of the lower extremity helps to judge the condition of the thrombosis and the effect of its treatment. The measurement of leg circumference is usually done at three points in the lower extremity: 1) the circumference of the ankle joint; 2) the circumference of the calf 10 cm below the knee; 3) the circumference of the thigh 15 cm above the knee, which is a comprehensive assessment of the entire lower extremity. Be sure to measure both sides at the same time, and measure every day for comparison, because when the thrombus is dislodged or thrombolytic therapy has an effect, the patient’s lower extremity will be significantly improved than before, and the swelling is also improved, so the treatment is effective.