Patients with infections in the department of critical care medicine have complex sources and diverse sites of infection, which may be associated with multiple pathogenic bacteria and have a high rate of drug resistance, posing a significant challenge to clinical diagnosis and treatment. Infections in the department of critical care medicine can be divided into two types: hospital acquired infections and non-hospital acquired infections, with significant differences in clinical characteristics between the two. This article discusses the relevant concepts, risk factors, pathogenesis, and common characteristics of severe infections such as bloodstream infections, pulmonary infections, intra-abdominal infections, and intracranial infections, as well as diagnostic and treatment plans and prevention and control strategies from the perspectives of hospital acquired and non-hospital acquired infections, aiming to provide valuable guidance for the clinical management of critically ill patients.