Objective To observe the effect of ultrasound-guided fascia iliac space block on anesthesia and postoperative pain in elderly patients undergoing hip arthroplasty. Methods From January 2018 to January 2021, a total of 80 elderly patients with hip replacement surgery were randomly selected and divided into two groups. Forty cases in the study group were treated with ultrasound-guided fascia iliac space block, and another 40 cases in the control group were not given fascia iliac space block. Pain score, Bromage score of affected limbs, and adverse reactions were evaluated at different time points after operation. Results The pain scores of the study group at 6, 12, 24 and 48 h after operation were lower than those of the control group （P<0.05）. At 2, 24, and 48 h after operation, there was no difference in Bromage score of motor block between the two groups （P>0.05）. The adverse reaction rate of the study group was lower than that of the control group （P<0.05）. Conclusion Ultrasound-guided fascia iliac space block in the treatment of elderly patients undergoing hip replacement surgery has a significant postoperative analgesic effect, and does not cause adverse reactions or affect the postoperative limb motor block, showing ideal prognosis.