Swollen legs and feet, i.e., edema of the lower extremities, are commonly seen in lower extremity deep vein thrombosis, heart disease, kidney disease and other pathological causes, but also in pregnancy, sedentary standing and other physiological conditions. 1. Pathological Lower extremity deep vein thrombosis: after the obstruction of venous return due to lower extremity thrombosis, the veins are stagnant and the vascular permeability increases, resulting in lower extremity edema. Heart disease: such as right heart failure, right heart failure when venous return is blocked, resulting in blood stagnation in the veins, causing elevated venous pressure, leading to the occurrence of lower limb edema. Kidney disease: when acute or chronic kidney disease occurs, it may affect the body’s water discharge, thus leading to the occurrence of lower limb edema. 2. Physiological Pregnancy: In the late stage of pregnancy, when the fetus is too big, the pressure on the inferior vena cava causes the obstruction of blood return, and edema of the lower limbs occurs. This is a normal physiological phenomenon, generally no treatment is needed, and most of the edema will disappear gradually after the end of pregnancy. Sitting and standing for a long time: the lack of contraction of the calf muscles to squeeze the blood back to the heart leads to the occurrence of leg and foot edema. In addition to the above factors, patients with hypothyroidism may also have lower limb edema, which requires prompt medical attention to clarify the cause of the disease and further examination and treatment under the guidance of the doctor.