As an important component of the body's intrinsic immunity，the barrier function of the skin plays a crucial protective role.The onset of many skin diseases is related to the damage of the barrier function of skin lesions，but the repair of the skin barrier always depends on the supplementation of continuous exogenous substances.The normal functioning of the qi-blood-liquid system maintains the homeostasis of the skin barrier function，and its disordered mechanism is the key pathogenesis of many skin diseases.Traditional Chinese medicine theory and modern physiology take the human body as the common cognitive object for the well-being of human health，both of them are one and the same.As a Qihuang scholar，Prof.Bai Yanping，on the basis of inheriting the experience of his predecessors and summarizing years of clinical experience，combined the “brick wall structure” of skin barrier function and proposed that essence and fluid are the “bricks” and “mortar” respectively to form the basic structure of skin barrier.Blood provides nutrient supply and discharges metabolic waste for the skin barrier，and qi plays the main defense function.Essence，qi，blood and fluid work together to maintain the normal functioning of the skin barrier，forming a theoretical model of skin barrier function with “essence and fluid as the base，blood as nourishment and qi as use”.The theoretical basis of the accompanying symptoms of skin diseases inside and outside the liaison has been explained，providing a more detailed theoretical basis for the treatment of skin diseases at the level of essence，qi，blood and fluids.