This paper introduces Professor Fu Yi's academic thought and clinical experience in the treatment of pulmonary arterial hypertension(PAH) by using the theory of "Pectoral Qi and Collaterals". As a difficult disease in modern medical diagnosis and treatment, PAH belongs to the category of "lung distension" in traditional Chinese medicine. Its clinical manifestations are characterized by chest tightness and shortness of breath, and aggravation of movement. Professor Fu Yi pointed out that the core of the pathogenesis of this disease lies in "Pectoral Qi deficiency and lung collateral stasis", forming a complex pathological pattern of "phlegm, blood stasis and deficiency". In the treatment, the core treatment principle of "Tonify and Elevate Pectoral Qi, Dispel Stasis and Free Collaterals " was created, and Shengxian Decoction combined with "Qilongtian" capsule was used for treatment, and combined with modern medical technology (such as right heart catheterization or echocardiography) to evaluate pulmonary artery systolic pressure as the basis for efficacy determination. In clinical practice, the use of "Qilongtian" capsule combined with Shengxian Decoction can significantly improve the symptoms and pulmonary circulation function of patients, and provide a new theoretical and practical path for the treatment of PAH in traditional Chinese medicine.