Abstract: Chest imaging examination plays an important role in the diagnosis, evaluation and prognosis of interstitial lung disease (ILD). However, the widely used chest high-resolution computed tomography (CT) can only reveal the extent and morphological characteristics of pulmonary lesions, but it can not reflect the pathophysiological process (inflammation or fibrosis) of pulmonary lesions. Recent studies showed that fibroblast activation protein (FAP) can be relatively specifically expressed in fibroblasts activated in fibrotic areas, and FAP inhibitor positron emission tomography (FAPI-PET) may reflect the degree of pulmonary fibrosis and the activity of fibroblasts, which has been used to evaluate the degree of fibrosis in various ILD. In this paper, the role and expression of FAP in pulmonary fibrosis and inflammatory tissue of ILD are reviewed, and the recent application of FAPI-PET in various ILD is summarized, which provides insight for the development of new imaging methods for the diagnosis and assessment of ILD.