The dynamic changes of inflammatory immunity in critically ill patients usually run through the occurrence and develop－ment of the disease. Immunoregulation under dynamic monitoring will be a future direction in the treatment of severe patients. Dexmedetomidine（DEX），a derivative of imidazole，is a strongly selective α2-adrenergic agonist with anti-anxiety，sedative and analgesic effects. Due to its combined analgesic and sedative effects and no obvious risk of respiratory depression，it is beneficial to cooperative or semi-conscious sedation in severe patients. It is usually used for mild to moderate sedation in intensive care unit and widely recognized. At the same time，DEX also has anti-inflammatory，antioxidant，anti-apoptosis and other immune regulatory effects，and has potential therapeutic value in severe patients with abnormal inflammatory immune state. At present，the immunomodulatory effects of DEX in sepsis，acute respiratory distress syndrome and other organ damage have attracted much attention. In this paper，the research progress of the immunomodulatory effects of DEX in severe patients and its mechanism are reviewed.