The causes of foot swelling in 90-year-old people are mainly in the following aspects: First, the elderly people with various organ function decline, especially cardiac insufficiency, cardiac hypoperfusion when the inferior vena cava reflux is blocked may cause swelling of the feet. Second, elderly patients with reduced digestive function, liver function, there may be hypoproteinemia caused by swelling of the feet. Third, elderly patients may be due to lower extremity venous thrombosis, inferior vena cava pressure and other conditions, resulting in venous reflux obstruction, elevated venous pressure resulting in swelling of the feet, if there is a unilateral lower extremity edema highly suspicious of the possibility of lower extremity venous thrombosis, as soon as possible for lower extremity venous ultrasound examination. In addition, there are also cases of foot swelling caused by renal insufficiency.