Objective To explore the viable protocol of dexmedetomidine combined sufentanil intravenous infusion for postoperative analgesia in elderly patients with total hip replacement. Methods The ninety elderly patients(age:65～89years)，ASAⅠ~ Ⅲ， with total hip replacement were randomly divided into 3 groups：①group of sufentanil (S) (n=30): sufentanil 0.04 ug·kg-1·h-1 and tropisetron 5 mg were dissolved in 120 ml normal saline for PCIA. ② group of dexmedetomidine 1(D1) (n=30): sufentanil 0.04 ug·kg-1·h-1, tropisetron 5 mg and dexmedetomidine 0.02 ug·kg-1·h-1 were dissolved in 120 ml normal saline for PCIA. ③group of dexmedetomidine 2 (D2) (n=30): sufentanil 0.04 ug·kg-1·h-1，tropisetron 5 mg and dexmedetomidine 0.05 ug·kg-1·h-1 were dissolved in 120 ml normal saline for PCIA . All patients’ anesthesia were performed by spinal block in L3-4. Sufentanil with 5 ug intravenous injection was administrated in all of groups 10 min before the end of operation. The patient controlled analgesia (PCA) program of all postoperative analgesia pumps was set with background infusion of 2 ml·h-1, a lockout of 15 min and a delivery of a bolus dose of 2 ml. The time of operation and anesthesia, amount of bleeding during operation, the incidence of adverse reactions ( pruritus, nausea and emesis) for postoperative analgesia, the BCS scores, and the consumptions of sufentanil for 48 h analgesia were recorded. In addition, VAS scores and Ramsay scores were also recorded at postoperative 4, 8, 12, 24, 48 h. Results At the 8~48 h after operation, the Ramsay score of group S was lower compared with group D1 and group D2（P<0.05, P < 0.01）; group D1 was no significant difference compared to group D2 . In assessment of the VAS score，group D1 was lower at the 12 h and 24 h after operation compared with group S（P < 0.05），but group D2 was lower at 8~48 h compared with group S（P<0.05）. In assessment of BCS score for 48 h analgesia, group D1 was higher than group S（P < 0.01）, and group D2 was significantly higher than all of group S and groupD1（P<0.01, P <0.05）. In Assessment of consumption of sufentanil for 48 h analgesia, the consumption of group S was apparently bigger compared with group D1 and group D2（P < 0.05，P < 0.01）. When group D2 compared with group D1,there was no significant difference. Conclusion The protocol of dexmedetomidine 0.05 ug·kg-1·h-1 combined sufentanil 0.04 ug·kg-1·h-1 intravenous infusion for postoperative analgesia in elderly patients with total hip replacement has better analgesic effect , greater patient satisfaction, reduces the total consumption of sufentanil and is safety and feasibility for clinical application.