Bronchiolitis obliterans in children is a rare chronic obstructive pulmonary disease with complex pathogenesis and poor prognosis. Based on the theory of underlying pathogenic factors, CHEN Wen-xia believes that the main pathogenesis of the disease is phlegm and blood stasis blocking collaterals and lung Qi stagnation. Exogenous evil Qi lies in the lung collaterals, consumes the healthy Qi secretly, dissolves phlegm into blood stasis, accumulates in the lung, blocks the airway, and can cause repeated coughing and wheezing. The main location of the disease is lung, involving the liver, spleen, kidney and other organs. It is not only the pathological product, but also the evolution process of pathogenesis. Therefore, it is suggested that the method of resolving phlegm and unblocking collaterals should be taken as the treatment method throughout the whole process. The treatment should be carried out by stages, and eliminate the latent pathogenic factors, eliminate the pathogenic factors and strengthen the body.