Objective:To investigate the effects of B ultrasound-guided lumbar plexus combined with sciatic nerve block on immune function, stress response, and postoperative analgesia in older adult patients undergoing hip surgery, providing theoretical evidence for clinical diagnosis and treatment.Methods:We included 300 older adult patients undergoing hip surgery who received treatment in Wenzhou Hospital of Integrated Traditional Chinese and Western Medicine from August 2018 to August 2019 in this study. We randomly allocated them into the observation and control groups ( n = 150/group). The control group was subject to general anesthesia and the observation group was subject to B ultrasound-guided lumbar plexus combined with sciatic nerve block. Hemodynamic changes and plasma cortisol levels were recorded in each group immediately after endotracheal intubation (T1), at 2 hours of surgery (T2), at the end of surgery (T3), and 24 hours after surgery (T4). Each patient's immune function was assessed 3 months after surgery. The Visual Analog Scale score at each time point was compared between the two groups. Results:The systolic blood pressure, diastolic blood pressure, and heart rate in the observation group at T1-T4 were (122.14 ± 8.68) mmHg, (117.41 ± 8.72) mmHg, (109.62 ± 8.43) mmHg, (127.82 ± 7.83) mmHg, (83.47 ± 6.32) mmHg, (72.34 ± 7.02) mmHg, (67.13 ± 6.72) mmHg, (74.15 ± 7.12) mmHg, (71.94 ± 7.64) beats/minute, (71.84 ± 7.11) beats/minute, (63.52 ± 6.16) beats/minute, (73.43 ± 7.29) beats/minute , respectively, which were significantly lower than those in the control group [(131.22 ± 8.69) mmHg, (125.81 ± 8.76) mmHg, (115.11 ± 8.44) mmHg, (133.26 ± 7.85) mmHg, (89.28 ± 6.12) mmHg, (77.64 ± 7.13) mmHg, (75.51 ± 8.02) mmHg, (81.13 ± 7.14) mmHg, (79.24 ± 7.65) beats/minute, (75.27 ± 7.13) beats/minute, (70.54 ± 6.22) beats/minute, (80.11 ± 7.32) beats/minute, t = 9.05, 8.32, 5.63, 6.00, t = 8.08, 6.48, 9.80, 8.47, t = 8.26, 4.17, 9.82, 7.91, all P < 0.001]. Plasma cortisol levels in the observation group at T2-T4 were (332.28 ± 15.64) ng/L, (334.67 ± 15.77) ng/L, (331.40 ± 15.68) ng/L, respectively, which were significantly lower than those in the control group [(344.75 ± 15.63) ng/L, (346.02 ± 15.76) ng/L, (345.83 ± 15.66) ng/L, t = 6.90, 6.23, 7.97, all P < 0.001]. At 3 months after surgery, the proportion of CD 4+ helper T cells, the proportion of CD 8+ cytotoxic T cells, and the ratio of proportion of CD 4+ Helper T cells to the proportion of cytotoxic CD 8+ T cells in the observation group were (31.39 ± 6.72)%, (25.73 ± 6.24)%, 1.31 ± 0.38, respectively, which were significantly lower than those in the control group [(38.61 ± 6.73)%, (32.79 ± 6.25)%, 1.52 ± 0.39, t = 9.29, 9.79, 4.72, all P < 0.001]. At 12-48 hours after surgery, The Visual Analog Scale scores in the observation group were (1.59 ± 0.54) points, (1.47 ± 0.33) points, (1.55 ± 0.41) points, respectively, which were significantly lower than those in the control group [(2.72 ± 0.55) points, (2.29 ± 0.36) points, (2.39 ± 0.43) points, t = 17.95, 20.56, 17.31, all P < 0.001]. Conclusion:B ultrasound-guided lumbar plexus combined with sciatic nerve block can effectively stabilize the hemodynamics in older adult patients undergoing hip surgery, reduce the occurrence of the stress response, promote the recovery of immune function, and alleviate pain.