Objective To investigate the effect of ultrasound guided block of pericapsular nerve(PENG)combined with lateral femoral cutaneous nerve(LFCN)on analgesia,stress response and postoperative cognitive function in patients undergoing hip replacement.Methods 102 patients who underwent hip Joint replacement in our hospital from September 2020 to September 2022 were selected and randomly divided into control group(51 cases)and study group(51 cases).The control group was given ultrasound guided iliac fascia space block(FICB),and the study group was given ultrasound guided PENG combined with LFCN block.The perioperative related indicators,postoperative analgesia effect,stress response indicators and postoperative cognitive function of the two groups were compared.Results There was no statistically significant difference in the comparison of surgical time between the two groups(P＞0.05).The amount of sufentanil used and the number of analgesic pump used within 48 hours after surgery in the study group were significantly lower than those in the control group(P＜0.05).The first postoperative time of getting out of bed and hospitalization in the study group were significantly shorter than those in the control group(P＜0.05).There was no statistically significant difference in VAS scores between the two groups at 6 h,12 h,24 h,and 48 h after surgery(P＞0.05).The VAS scores of the study group were significantly lower than those of the control group at 6 h,12 h,and 24 h after surgery(P＜0.05).The heart rate(HR)and Mean arterial pressure(MAP)of the control group were higher at the time of block(T1),30 min of block(T1)(T2),and the end of block(T3)than at the time of entry(T0)(P＜0.05).HR and MAP of the study group were significantly lower than those of the control group(P＜0.05).The MMSE scores of the two groups at 6 h,12 h,24 h,and 48 h after surgery were lower than those before surgery(P＜0.05),but the MMSE scores of the study group were significantly higher than those of the control group(P＜0.05).Conclusion Using ultrasound guided PENG combined with LFCN block for patients undergoing hip Joint replacement can more effectively reduce the amount of opioids and the number of use of analgesia pump,reduce postoperative pain in the exercise state,reduce stress reaction,and have less impact on cognitive function,so as to promote faster recovery of patients.