This paper aims to discuss etiology, pathogenesis and principle of treatment of pulmonary interstitial fibrosis, and propose differentiation at different stages. In the early stage it should be treated in dispersing Lung-Qi while in the middle stage it should be treated in dissipating phlegm and in the late stage it should be treated in strengthening the body resistance to eliminate pathogenic factors. We can achieve bette  Results: by treatment based on syndrome differentiation.