Professor Cai Wanru believes that in the stable phase of chronic obstructive pulmonary disease, "phlegm" and "stasis" are intertwined, with "phlegm" as the main component. Disease is manifested mostly in the lungs, spleen and kidney, and along with the duration of the disease, the patients are prone to "sputum", "stasis" and other pathological products, so that acute aggravating symptoms are often induced due to the transformation from "phlegm" to "stasis". The clinical manifestations are mainly the lack of righteousness, and various symptoms due to phlegm stagnation and blood stasis. Therefore, Professor Cai believes that the thought of "preventive treatment of disease" should be throughout the treatment of the disease. The thought is based on the principle of the relationships between the five internal organs. According to the characteristics of disease transmission, combined with the syndrome differentiation of physical constitution, the importance of strengthening the body resistance and nourishing the vigour was emphasized. In terms of the methods of treatment, methods such as nourishing the lungs and tonifying the spleen, warming the kidney and tonifying qi are often applied, so the prescription is flexible and the compatibility is rigorous. In terms of the control of symptoms and prevention of acute exacerbations, it has a significant effect. Therefore, the thought of "preventive treatment of disease" proposed by Professor Cai Wanru has a practical value in the clinical treatment of chronic obstructive pulmonary disease, which is worthy of promotion.