Background　In recent years, dexmedetomidine (Dex) is more and more widely used in the treatment of delirium, but its mechanism of action is not well known.　Objective　Provide a theoretical basis for the application of Dex in the treatment of delirium.　Content　Describe the mechanism of Dex in the treatment of delirium and its clinical effect in postoperative and intensive care unit patients.　Trend　At present, a lot of literatures and clinical applications suggested that Dex is effective in the treatment of delirium, but the best way and best dosage of using that need further study.