Immune checkpoint inhibitor associated pneumonia (CIP) is a common immune related adverse reaction, accounting for 35% of all deaths. However, due to the lack of typical clinical symptoms and imaging manifestations, CIP needs to be differentiated from other diseases such as pulmonary infections and lung cancer progression. Currently, there is a lack of diagnostic gold standards, which belongs to exclusive diagnosis. Empirical diagnosis and treatment in clinical practice can easily lead to the abuse of hormones and antibiotics, and even misdiagnosis and mistreatment, resulting in patient death. Therefore, early identification of CIP and pulmonary infection is the key to successful diagnosis and treatment. The CIP diagnosis and treatment guidelines recommend performing bronchoalveolar lavage as appropriate, but there is still a lack of large-scale prospective clinical studies. The beneficial pathogen metagenomic sequencing technology for the diagnosis of pulmonary infections has not been mentioned. Our research group conducted a prospective clinical study for the first time to evaluate the effectiveness and safety of bronchoalveolar lavage combined with pathogen metagenomic sequencing technology in diagnosing CIP, explore biomarkers for diagnosing CIP, in order to improve the early diagnosis rate and treatment efficiency of CIP, and reduce the abuse of antibiotics and hormones.