OBJECTIVE： To study the effects of dexmedetomidine on general anesthesia analgesia of lumbar spinal surgery and postoperative cognitive function in elderly patients. METHODS： 64 patients underwent lumbar spinal surgery were randomly divided into observation group and control group with 32 cases in each group. Both group were routinely given fentanyl and cisatracurium for anesthesia induction； observation group was additional given intravenous injection of dexmedetomidine before and after anesthesia induction； control group was additionally given same volume of 0.9％ sodium chloride injection with intravenous injection. The serum concentration of adrenocortical hormone was detected before surgery （T0）， 2 h after surgery began （T1）， 24 h after surgery （T2）； VAS was used for analgesic effect evaluation 2， 8 and 24 h after surgery； MMSE was used to evaluate cognitive function 1 and 2 d after operation， and the incidence of POCD was calculated. The occurrence of ADR was observed. RESULTS： The serum concentration of adrenocortical hormone in observation group was significantly lower than in control group at T1， with statistical significance （P＜0.05）. VAS score of observation group 2 h after surgery were significantly lower than that of control group， with statistical significance （P＜0.05）； there was no statistical significance in VAS score 8 and 24 h after surgery （P＞0.05）； the incidence of POCD in observation group was significantly lower than in control group 1 and 3 d after surgery， with statistical significance （P＜0.05）. No anesthesia-related ADR was found except POCD. CONCLUSIONS： Dexmedetomidine has strong antioxidant capacity， can effectively reduce oxidative stress in elderly patients during lumbar spinal surgery， and reduce the incidence of POCD.