Abstract: Objective To investigate the effect of intravenous infusion of aminophylline on lung function and postoperative pulmonary complications (PPCs) in elderly patients under total hip arthroplasty. Methods A total of 279 elderly patients who were scheduled for total hip arthroplasty under general anesthesia were enrolled. They were randomly divided into three groups: a control group (group C, n=93), an aminophylline 2.5 mg/kg group (group A1, n=94), and an aminophylline 5 mg/kg group (group A2, n=92). Group A1 was intravenously infused with 2.5 mg/kg of aminophylline immediately after anesthesia induction over 30 min. Group A2 was intravenously infused with 5 mg/kg of aminophylline at the same time point. Group C received the same volume 5% glucose solution. All patients underwent routine general anesthesia. Patients in the three groups were compared for blood gas analysis before anesthesia induction (T0), 0.5 h after mechanical ventilation (T1), 1 h after mechanical ventilation (T2), and after surgery (T3). Meanwhile, the lung dynamic compliance (Cd) and static compliance (Cs), oxygenation index (OI), and alveolar-arterial oxygen difference (A-aDO₂) were calculated according to the corresponding respiratory parameters. Meanwhile, their mechanical ventilation time, surgical time, intraoperative fluid infusion, blood transfusion, recovery time, extubation time, the quality of postoperative recovery, and PPCs within seven days after surgery were also recorded. Results There were no statistical differences in OI and A-aDO₂ at T0 among the three groups. At T2 and T3, groups A1 and A2 showed remarkable increases in OI, Cd and Cs, and decreases in A-aDO₂, compared with group C (P<0.05); group A2 showed remarkable increases in OI, Cd and Cs, and decreases in A-aDO₂, compared with group A1 (P<0.05). Compared with group C, the incidence of PPCs in group A1 and group A2 was significantly reduced,and the incidence of PPCs in group A2 was lower than that in group A1 (P<0.05). Compared with group C, group A1 and group A2 presented significantly shortened recovery time and extubation time, with a reduced incidence of hypoxemia after extubation (P<0.05), and statistical differences were found between group A1 and group A2. The quality of recovery-15 (QoR-15) scores in groups A1 and A2 were significantly higher than that in group C (P<0.05). There was no significant difference in the incidence of postoperative nausea and vomiting among the three groups. Conclusions Intravenous infusion of aminophylline can obviously improve the perioperative pulmonary ventilation and gas exchange in elderly patients undergoing total hip arthroplasty, significantly reduce the incidence of PPCs in patients, and improve the quality of recovery.