With the continuous development and maturity of anti-tumor immunotherapy technology, immune checkpoint inhibitors as one of the main methods of immunotherapy were increasingly widely used in clinical tumor cases, bringing new hope for many advanced cancer patients with poor response to traditional treatment, but at the same time, reported on adverse reactions of various organs related to this were also increasing, and the immune damage caused by them was harmful to patients, especially immune checkpoint inhibitor-associated pneumonia, immune checkpoint inhibitor-associated myocarditis and immune checkpoint inhibitor-associated encephalitis, which could even seriously endangered the lives of patients. Therefore, it was necessary for clinicians to fully understand and master the mechanism, clinical characteristics, laboratory and imaging examination characteristics, diagnostic criteria and differential diagnosis conditions, and treatment principles of adverse reactions that may be caused by immune checkpoint inhibitors, so as to find a more optimized anti-tumor treatment regimen and actively prepared for the treatment of possible immune-related adverse reactions. In this paper, we reported a case of immune checkpoint inhibitor-associated severe pneumonia, referred to the relevant guidelines, introduced its clinical features, laboratory and imaging findings, difficulties encountered in the diagnosis and treatment process, briefly analyzed the causes, and reviewed the possibility of immune-related pneumonia should be considered when respiratory symptoms occurred in patients receiving immunotherapy; the increased ratio of blood neutrophil count to lymphocyte count, and the increased ratio of eosinophil count to lymphocyte count could be used as indicators to indicate immune-related adverse reactions in patients; bronchoalveolar lavage fluid examination and bronchoscopy and lung biopsy were helpful for the diagnosis; when immune checkpoint inhibitor-associated severe pneumonia occurred, in addition to symptomatic and sup-portive treatment, adequate glucocorticoid-based immunosuppressive therapy should be given in time, and combined with cytokines monoclonal antibodies and other biological agents, immunoglobulin co-therapy, but the current indications for the use of biological agents were not fully clear, and the use of high-dose immunosuppressive drugs might cause the risk of severe infection. Therefore, according to the relevant literature and the findings in the process of clinical diagnosis and treatment, this paper proposed that the serum levels of IL-6, TNF-α, CRP and other inflammatory mediators in patients may be used as a quantitative indication to initiate biological agent therapy and accumulate experience for better solving similar problems in the future.