The majority of the swelling in the legs and feet after sitting for a long time is due to the edema of the lower limbs caused by poor blood flow back to the lower limbs after sitting for too long. Poor blood flow to the lower extremities is common in the elderly, bilateral lower extremity vascular atherosclerosis, elasticity is damaged to a certain extent, at the same time the venous valve function is damaged, the blood in the veins can not smoothly flow back to the heart, so the lower extremities are prone to venous blood stagnation, thus appearing edema situation. When this happens, the lower limbs need to be elevated so that the blood can flow back smoothly, and in this case, the occurrence of lower limb edema can be reduced. If this condition is ruled out and edema occurs in the lower extremity, especially if the edema occurs unilaterally, it may be thrombosis, and a lower extremity vascular ultrasound is needed for differential diagnosis.