Swelling of legs may be the precursor of lower extremity venous thrombosis, hypoproteinemia, heart failure, kidney disease, thyroid insufficiency, anaphylactic purpura and other diseases. 1. Lower extremity venous thrombosis: Lower extremity deep vein thrombosis leads to lower extremity blood return obstacle will cause lower extremity swelling. 2. Hypoproteinemia: due to the decrease of colloid osmotic pressure, edema is caused and the symptoms of leg swelling appear. 3. Heart failure: patients with heart failure will have symptoms of swollen legs. 4. Kidney disease: due to abnormal kidney function, the kidney drainage ability decreases, resulting in leg swelling. 5. Thyroid insufficiency: it can lead to mucous edema, and then the symptoms of leg swelling. 6. Anaphylactic purpura: In addition to the appearance of purpura, anaphylactic purpura may be accompanied by neurogenic edema, which leads to leg swelling. Patients with leg swelling, persistent unrelieved, should be timely hospital consultation, clear cause, under the guidance of the doctor for treatment.