Abstract：The key mechanism of combined allergic rhinitis and asthma syndrome in children is “deficiency of the root” and “the contraction of pathogens”. Deficiency of the root is the internal cause， which is mainly manifested by the dysfunction of the lung，spleen and kidney. Contracted pathogens are mainly wind and cold，which is the external condition of combined allergic rhinitis and asthma syndrome. Xiaoxuming tang has the effect of tonifying the lung and fortifying the spleen， warming yang and resolving fluid retention as well as releasing the exterior and dissipating cold. Its prescription is completely consistent with the mechanism of allergic rhinitis and asthma syndrome，which are “deficiency of the root” and “the contraction of pathogens”. Clinical application of Xiaoxuming tang for combined allergic rhinitis and asthma syndrome in children can achieve a good curative effect.