The prevalence of diabetes is increasing and the risk of pulmonary infection among patients with diabetes mellitus is higher than that among people without diabetes mellitus.The clinical characteristics and prognosis of pulmonary infection patients with diabetic are also distinct from that of patients without diabetic.To improve the level of clinical diagnosis and treatment,it's important to understand the mechanisms of pulmonary infection in diabetic patients and to be familiar with the clinical manifestations of bacterial,fungal and viral infections in them.