Abstract： Acute-on-chronic liver failure (ACLF) is a clinical syndrome characterized by chronic liver disease, multiple organ failure and high mortality. ACLF patients have a high incidence of concurrent infection due to immune dysfunction. Early diagnosis of concurrent infection can initiate early anti-infection treatment and improve patient prognosis. However, ACLF complicated with infection is easy to be misdiagnosed, so searching for new diagnostic methods and biomarkers of infection can improve the reliability and accuracy of diagnosis. This article reviews the progress on epidemiology and immune-related characteristics, and their effect on diagnosis of concurrent infection in patients with ACLF.