Interstitial lung disease (ILD) is a group of diffuse lung diseases that mainly involve the interstitium, alveoli, and/or fine bronchi. The main clinical manifestations are progressive exertional shortness of breath, restrictive ventilation dysfunction with reduced diffusion function, hypoxemia, and diffuse bilateral lung lesions on imaging. The disease course is mostly insidious, slowly progressive and has a poor prognosis. Early diagnosis and early intervention are the keys to improve the prognosis. The methods of early diagnosis of interstitial lung lesions are summarized as follows. 1.High-resolution CT (HRCT): Given that X-ray examination is not sensitive to ILD and about 80% of ILD is missed by chest X-ray, it is necessary to improve the early diagnosis of ILD with more sensitive and specific examination. The most important progress in recent years is to make HRCT the first choice for the diagnosis of ILD, with a sensitivity of up to 80%, and the imaging classification of ILD according to the different manifestations of HRCT (such as honeycomb-like changes, ground glass-like changes, grid shadow and solid shadow, etc.), so as to deduce its corresponding pathological classification and help clinical selection of treatment plan and assessment of prognosis. 2. Pulmonary function tests: force spirometry (FVC) and carbon monoxide dispersion (DLCO) are indispensable tests for ILD, which are even more sensitive than HRCT for the detection of early lesions, with the drawback that they are not intuitive enough. For ILD with the same type of pathology, the difference in lung function reflects the difference in prognosis, i.e. the worse the lung function the worse the prognosis, after treatment the lung function improves and the patient’s survival improves. Therefore, monitoring lung function can not only effectively determine the prognosis of patients, but also help to assess the response to treatment. 3. Lung biopsy: Pathology is the gold standard for the diagnosis of ILD. Although CT and pulmonary function tests can confirm the diagnosis in most patients with ILD, there are still some patients who lack specific clinical signs and still need lung biopsy for proper diagnosis. Classical open lung biopsy is more traumatic, not easy for patients to accept, and rarely carried out clinically; thoracoscopic lung biopsy rarely causes acute complications common to open lung biopsy, and at the same time, satisfactory sampling is the most recommended method; CT-guided percutaneous lung puncture is less invasive, can pre-determine and adjust the angle and depth of the needle, and has a high safety, but not enough sampling, and its application value is still controversial. 4, the detection of inflammatory factors: transforming growth factor (TGF)-β, complexine kinase c-Abl, serum lung surface active protein (SP)-A, SP-D and small fossa protein-1 and many other inflammatory factors involved in the pathogenesis of ILD, they are all important biomarkers affecting the response to pulmonary fibrosis, the determination of these inflammatory factors can help the diagnosis of ILD, especially the combined examination of multiple factors The compliance rate is significantly better than the application of individual indicators. The early diagnosis of ILD also relies on important clues such as a detailed history of occupational exposure, onset, concomitant symptoms, past medical history and treatment history. Occupational dust exposure can take 10-20 years before symptoms of ILD appear. In contrast, in rheumatic diseases, ILD can be present first, followed by lesions of joints or other organs; or other lesions of rheumatic diseases can be present first, followed by clinical manifestations of ILD. Rheumatic diseases that are prone to ILD include rheumatoid arthritis, dry syndrome, systemic sclerosis, inflammatory myopathy, mixed connective tissue disease, systemic lupus erythematosus, polyarteritis nodosa, Wegener’s granulomatosis, etc. For these patients, HRCT can be performed when necessary to clarify the presence of interstitial lung disease associated with connective tissue disease as early as possible. For these patients, HRCT is necessary to identify the occurrence of interstitial lung disease associated with connective tissue disease (CTD-ILD) as early as possible.