Legs turn purple when standing still because of the presence of lower extremity venous reflux obstruction. In the vast majority of patients, lower extremity venous valve insufficiency can be detected by ultrasound during lower extremity venous examination. Valves are the equivalent of small valves in the blood vessels. When blood flows from the feet to the heart, the valves will open and close, and when the valves are not closed properly, the blood will reflux from the heart back into the veins of the lower extremities, resulting in high pressure and stagnation of blood in the veins of the lower extremities. This condition is often aggravated by the weakening of the muscle pump of the calf after standing for a long time, so it will appear purple. Once this condition occurs, it should be diagnosed and treated at an early stage in order to avoid gradual aggravation of the disease.