Objective To observe the clinical effects of ultra-sound guided lumbar plexus and sciatic plexus nerve block combined with general anesthesia on elderly patients undergoing hip replace-ment surgery.Methods Eighty elderly patients scheduled for unilateral hip replacement surgery were randomly divided to lumbar plexus and sciatic plexus nerve block combined with general anesthesia group (group N)and general anesthesia group (group G).The airways of all the patients were con-trolled by laryngeal mask airway (LMA)in both groups.The bispectral index (BIS)of patients in both groups was maintained in the range of 45-55.The dosage of sulfentanyl,visual analogue scale (VAS)at 2,4,8 and 24 h after surgery,and the dosage of patient controlled analgesia (PCA)drugs were recorded.The period from end of surgery to extubation,off-bed activity and discharged from hospital,mortality in 30 days after surgery were recorded.Meanwhile,postoperative delirium (POD) and postoperative cognitive dysfunction (POCD),and severe cardiovascular and pulmonary complica-tions were evaluated.Results No patient died in 30 days after surgery in both two groups.One patient suffered from severe pulmonary infection in group G.The dosage of sulfentanyl of group N was less than the value of group G (P <0.05),the periods from end of surgery to extubation,off-bed activity and discharged from hospital of group N were shorter than those in group G (P <0.05 ).The VAS scores and incidence of POD and POCD in group N were lower than those in group G (P < 0.01 ). Conclusion In elderly patients undergoing hip replacement surgery,ultrasound-guided lumbar plexus and sciatic plexus nerve block combined with general anesthesia could help reduce usage of opioids during operation,offer better analgesia effect,shorten the period of off-bed activity and discharged from hospital and reduce incidence of POD and POCD in elderly patients.