For sudden swelling of the calf, especially unilateral swelling of the calf, deep vein thrombosis of the lower limbs, including intermuscular vein thrombosis, is highly suspected. In this case, ultrasound should be performed as early as possible to determine whether there is a thrombus in the blood vessel, and at the same time, D-dimer examination, and a combination of the two judgments basically makes clear the existence of a thrombus. Thrombus may lead to pulmonary embolism, which is life-threatening, so once this situation occurs, it must be treated as soon as possible. If venous thrombosis in the calf is ruled out, valvular insufficiency is considered. However, swelling due to valvular insufficiency tends to be chronic and persistent, and in this case only compression stockings are needed to avoid further aggravation of the disease.