In clinical practice, many patients with pulmonary fibrosis ask what causes the disease. Pulmonary fibrosis (PF) is an injury to the lung caused by a variety of factors, mainly alveolitis and interstitial pneumonia in the early stages, and eventually pulmonary fibrosis. The clinical manifestations are active dyspnea, restrictive ventilation, reduced diffusion and hypoxemia, and often death due to respiratory failure. The causes of the disease are complex and not yet well understood. Genetic abnormalities in surface active protein have been reported in the literature to be associated with PF. 2, viral factors: the lung is an open organ, and the outside world, viruses can easily invade, causing inflammation, resulting in damage, repair, and fibrosis. The newly occurred SARS and avian influenza virus infection can cause lung damage, thus further confirming that lung damage and pulmonary fibrosis are related to viruses. The viral pathogenesis is not only related to its proliferation, but also recently it is believed to be closely related to the proteins it expresses. The S-glycoprotein plays a key role in the pathogenesis of viruses, mediating the entry of viruses into target cells, inducing immune responses, determining the level of viral replication, and inducing inflammation; the N-protein initiates the translation of viral proteins, inhibits the translation of host cell MHCI-like molecules and other proteins, and releases inflammatory factors, leading to the pathological process of viral infection, which can eventually cause pulmonary fibrosis. 3, immune abnormalities: the pathogenesis of pulmonary fibrosis is very complex, has not been fully elucidated, but the involvement of the immune response is a major aspect of the formation of pulmonary fibrosis. Cytokines such as IL-6 have a wide range of biological functions and are closely related to the formation of pulmonary fibrosis, and their abnormal secretion or abnormal gene expression can lead to a series of diseases such as pulmonary fibrosis. 4, environmental pollution: including organic, inorganic dust, oxidizing gases, etc.. Organic dust such as farmers’ lung, pigeon lung, cane dust lung, etc., inorganic dust in the working environment such as various mining dust, automobile exhaust, micro dust, silica dust, asbestos fibers, etc. can cause lung damage leading to pulmonary fibrosis diseases such as pneumoconiosis, pneumoconiosis is the most serious occupational disease in China, of which the incidence of silicosis is the highest; inhalation of automobile exhaust, high-pressure oxygen and ozone and other oxidizing gases, can also cause lung damage leading to pulmonary fibrosis. These results have been confirmed in animal experiments. 5, Drugs and chemicals: Bleomycin is an antineoplastic agent with a restrictive toxicity of PF. It is now used as a classical model for studying pulmonary fibrosis. Amiodarone is a highly effective and widely used antiarrhythmic agent, but it has many adverse effects, the most serious of which is pulmonary fibrosis. Other drugs such as: antibiotics, NSAIDs, cyclophosphamide, leflunomide, paraquat, oral hypoglycemic agents, penicillamine, colchicine, and certain banned drugs. 6.Physical damage: Radiotherapy is one of the three major treatments for tumors. As radiation therapy is widely used in the treatment of lung, esophagus, mediastinum and other parts of the tumor and the pretreatment of bone marrow transplantation, the accompanying side effect of radiation pulmonary fibrosis is becoming a prominent problem. Prolonged high concentrations of oxygen can also lead to lung damage and pulmonary fibrosis. 7, Secondary to other diseases: Most commonly secondary to connective tissue disease. Other interstitial diseases such as pulmonary infection-related diseases, liver disease, intestinal disease, chronic heart disease, renal insufficiency, organ transplantation, etc. can occur in combination with interstitial lesions. In conclusion, the lung is very sensitive to a variety of injury factors, which can damage the lung individually or simultaneously, and it is difficult to identify the specific, major factors, which can cause repeated lung repair over time, leading to pulmonary fibrosis. Therefore, the etiology of pulmonary fibrosis is diverse and complex, and needs to be studied in depth.