Abstract: Objective To investigate the effect of hydromorphone combined with different doses of dexmedetomidine on postoperative analgesia in elderly patients undergoing laparoscopic radical prostatectomy. Methods Seventy-five elderly patients undergoing laparoscopic radical prostatectomy were randomly divided into three groups(25 cases in each group):Group H,Group HD₁ and Group HD₂.All patients were given intravenous analgesia pump with 20 μg/kg hydromorphone by intravenous injection 30 minutes before the surgery was finished.0.1 mg/kg hydromorphone and normal saline to 100 ml for Group H,hydromorphone 0.1 mg/kg combined with dexmedetomidine 2 μg/kg and normal saline to 100 ml for Group HD₁,and hydromorphone 0.1 mg/kg combined with dexmedetomidine 4 μg/kg and normal saline to 100 ml for Group HD₂.The recovery time,time to extubation,residence time of resuscitation,VAS scores and Ramsay scores at 1 h(T₁),6 h(T₂),12 h(T₃),24 h(T₄),36 h(T₅),48 h(T₆) after the operation and adverse events were monitored and recorded.The the time to first flatus and occurrence of side reaction such as nausea and vomiting,skin pruritus,respiration inhibition,bradycardia,hypotension and dry mouth were also investigated. Results There were no statistical significance among the three groups in the difference of recovery time,time to extubation,the residence time of resuscitation and the Ramsay scores(P>0.05).The VAS scores in both group HD₁ and group HD₂ were significantly lower than that in group H.The occurrence of dry mouth and hypotension in group HD₂ was significantly higher than that of both group H and group DH1,the others about adverse reaction were on significance difference among the three Groups. Conclusion It is effective and have less adverse reactions to use hydromorphone combined with 2 μg/kg dexmedetomidine in postoperative analgesia for the elderly patients undergoing laparoscopic radical prostatectomy.We consider that it is worth recommending.