Deficiency of Wei Qi refers to the deficiency of Yang Qi outside the body that cannot fix the surface, and the skin couples are easy to be invaded by external evil and get sick. Wei Qi has the function of warming the skin, opening and closing the pores, regulating cold and temperature, and resisting disease-causing factors. If Wei Qi is deficient, it cannot fix the surface and the skin couples are loose, so disease-causing factors can easily invade the body. Clinical manifestations mainly include frequent colds, excessive spontaneous sweating, sweating out of evil wind, slight fever, headache, nasal congestion, or sweating out of more than one, sweating out of evil wind, small amount of urine and weakness, tiredness of limbs, white tongue coating, etc. The treatment method is to tonify the qi and fix the surface or combine with astringent yin to stop sweating, and the prescription usually uses Yu Ping Feng San, which consists of Huang Qi, Bai Zhu, Fang Feng and so on, with the addition and subtraction of treatment according to the evidence.