Abstract： With the influence of environment,heredity and other factors,the prevalence of chest imaging screening has significantly increased the detection rate of pulmonary nodules.This paper introduces various causes of pulmonary nodules,including infectious and non-infectious pulmonary nodules,infectious pulmonary nodules including bacteria,fungi,viruses and other pathogens,and non-infectious pulmonary nodules including sarcoidosis,vasculitis,tumors and others.The formation mechanism of various pulmonary nodules,involving various cytokines,inflammatory mediators,transporters and signaling pathways,was briefly reviewed.Most of the pathological mechanisms of pulmonary nodules are attributed to factors such as chronic inflammation,immune response or malignant proliferation caused by gene mutation.Analysis shows that the occurrence and development of pulmonary nodules are basically caused by antigen presentation,cell phagocytosis and processing of antigens,release of cytokines,and aggregation of lymphocytes and monocytes,and infectivity is relatively common.Therefore,to grasp the occurrence and formation mechanism of pulmonary nodules,early intervention can reduce the occurrence of pulmonary nodules,and provide references for clinical diagnosis and treatment.