The lesions of varicose veins mainly occur in the middle layer of vein wall. The early thickening of elastic tissue and muscle tissue in the middle layer can be regarded as a compensatory reaction caused by the increase of venous pressure. In the later stage, both muscle tissue and elastic tissue atrophy and disappear, and are replaced by fibrous tissue, and the vein wall becomes thinner, loses elasticity and expands. The venous valve also atrophied and hardened. The microcirculation of the tissues around the diseased vein is also disturbed by the increase of venous pressure, resulting in malnutrition and fibrous cell proliferation. The subcutaneous tissue of the lesion site is diffuse fibrosis with edema, and the edema fluid contains a large amount of protein, which can cause fibrous tissue hyperplasia. Venous congestion hinders lymphatic reflux, and lymph contains a lot of protein, which aggravates tissue fibrosis. The result of such a vicious circle is local tissue hypoxia, reduced anti-injury ability, and prone to infection and ulcer.