There are several possible causes of swollen legs after standing for a long time: first, venous thrombosis of the lower extremities, when venous thrombosis can occur after standing for a long time, the symptoms of swollen legs after standing for a long time should be diagnosed and treated with venous ultrasound or angiography of the lower extremities. Secondly, phlebitis and varicose veins of lower limbs, phlebitis and varicose veins can lead to obstruction of venous return and swollen legs after standing for a long time, which should be diagnosed and treated by examination of lower limbs and ultrasound examination of superficial veins of lower limbs. Thirdly, lower extremity venous reflux disorder is common in elderly people, due to poor peripheral circulation in elderly people, which leads to swollen legs after standing for a long time, and it should be combined with the patient’s age and physical examination to exclude other diseases for early diagnosis and treatment.