Dexmedetomidine，as a highly selective α2-adrenergic receptor agonist. Its pharmacological effects include sympathetic inhibition，sedation，hypnosis，anti-anxiety. It can also protect central nervous system and reduce the incidence of postoperative cognitive dysfunction. Some studies believe that dexmedetomidine can reduce the stress response，inhibit the inflammatory response，reduce the release of inflammatory factors and improve the postoperative cognitive function of patients. In this paper，the effect of dexmedetomidine on postoperative cognitive dysfunction will be discussed.