Objective To investigate the effects of applying pressure ⁃controlled and volume ⁃guaranteed ventilation mode during prolonged robotic⁃assisted laparoscopic surgery in the Trendelenburg position on patients′ respiratory mechanics and pulmonary function. Methods Seventy ⁃six patients undergoing elective robot ⁃assisted laparoscopic lower abdominal surgery were selected and randomly divided into pressure⁃controlled volume⁃guaran⁃ teed ventilation group（group P）and volume ⁃controlled ventilation group（group V）. The peak airway pressure， airway plateau pressure，dynamic lung compliance and airway resistance were recorded immediately after induction （T2），20 min（T3），1 h（T4），2 h（T5）and 3 h（T6）after pneumoperitoneum，and 10 min after extubation（T7）； the oxygenation index and intrapulmonary shunt rate were recorded before induction（T1），T2⁃T7，and 20 min after extubation（T8）；the postoperative pulmonary complication rate，and pulmonary atelectasis was assessed by ultra⁃ sound at T1，T8，and on postoperative days 1 and 3. Results Respiratory mechanics：compared with T2，the differences in peak airway pressure，plateau pressure，airway resistance and dynamic lung compliance during pneumoperitoneum（T3⁃T6）in both groups were statistically significant（P < 0.05）；compared with group V，peak airway pressure and plateau pressure in T3 ⁃ T7 and airway resistance in T3 ⁃ T6 in group P were significantly lower （P < 0.05），and lung compliance was significantly higher except for T2 and T3（P < 0.05）. Lung function：com⁃ pared with T1，there were significant differences in the changes of oxygenation index and intrapulmonary shunt rate from T2 to T7 in both groups（P < 0.05）；compared with group V，the intrapulmonary shunt rate from T4 to T6 and oxygenation index from T5 to T6 in group P were significantly lower（P < 0.05）. There was no significant difference in the incidence of postoperative complications between the two groups（P > 0.05）；the degree of postoperative pul⁃monary atelectasis was significantly lower in group P compared with group V（P < 0.05）. Conclusion Compared with volume⁃controlled ventilation，pressure⁃controlled and volume⁃guaranteed ventilation could reduce peak airway pressure，plateau pressure and airway resistance，improve lung compliance，oxygenation and intrapulmonary shunt，and reduce postoperative pulmonary atelectasis，and has advantages when applied to prolonged Trendelen⁃ burg position robotic⁃assisted laparoscopic surgery.