Objective To investigate the effect of preoperative intravenous infusion of dexmedetomidine combined with ultrasound-guided lumbosacral plexus block in elderly patients undergoing hip replacement surgery.Methods Eighty elderly patients with hip fracture were treated with hip replacement surgery.They were divided into 2 groups:groupⅠand groupⅡ.Patients in groupⅠreceived general anesthesia,and patients in groupⅡreceived venous anesthesia combined with ultrasound-guided lumbosacral plexus block.The VAS scores of the two groups in 48 hours after surgery,the expression of S100-βand NSE,and the incidence of POD within 7 days after surgery were observed.Results The VAS scores of groupⅡwere significantly lower than those of groupⅠat 2,6,12,24 and 36hours after operation(P<0.05).The expressions of S100-βand NSE in groupⅡwere significantly lower than those in groupⅠat each time point after operation(P<0.05).The incidence rate of POD in groupⅡwas significantly lower than that in groupⅠ(P<0.05).Conclusion Dexmedetomidine combined with ultrasound-guided lumbosacral plexus block used in elderly patients undergoing hip arthroplasty has good analgesic effect and improved postoperative cognitive function,which is worthy of clinical promotion and application.