Abstract： The theory of eight- principle syndrome differentiationdivides diseases into exterior and interior syndromes according to the depth of disease location． When exogenous pathogens invade the human body， the disease location is superficial,and this usually constitutes exterior syndrome． The two common points between skin mucosal infection and exterior syndrome are the depth of location and invasion of exogenous pathogens．When pathogenic organisms invade skin and mucosa and show dominant infection， there are mainly three manifestations： exterior syndrome in a broad sense without fever and aversion to cold， exterior syndrome in a narrow sense， and interior syndrome． After using the classification statistics of the diseases of skin mucosal infection in the current medical textbooks， it is found that the total number of diseases is 124，of which 116 were exterior syndrome in a broad sense (94%)，76 exterior syndrome in a narrow sense (61% )， and 68 interior syndrome (55% )． Skin mucosal infection is closely related to exterior syndrome： the initial stage of skin mucosal infection usually forms exterior syndrome in a broad sense，andif the development of the disease is accompanied by fever and aversion to cold，exterior syndrome in a narrow sense is formed，and what's more，only in a few cases，the interior syndrome occurs only after the disease goes further.