Objective To investigate the effects of different arterial partial pressure of carbon dioxide (PaCO₂) on regional cerebral oxygen saturation (rScO₂) in robot assisted laparoscopic pyeloplasty (RALP) in children. Methods Forty-five children who received RALP in Pediatric Urology Department of the Seventh Medical Center of Chinese PLA General Hospital from February 2019 to February 2020 were selected as the study subjects, by adjusting tidal volume and respiratory rate maintained PaCO₂ at 35-45 mmHg (group N), 30-34 mmHg (group M) and 25-29 mmHg (group L) with 15 patients in each group. Before anesthesia (T₀), 10 min after endotracheal intubation (T₁), before lateral decubitus surgery (T₂), 30 min after pneumoperitoneum(T₃), 10 min after pneumoperitoneum (T₄), and 10 min after recumbent position (T₅), rScO₂ of affected side, percutaneous pulse oxygen saturation (SpO₂), heart rate (HR), mean arterial pressure (MAP), pharyngeal temperature (T), pH and hemoglobin (Hb)were recorded respectively. Arterial blood was extracted for blood gas analysis, and PaCO₂ was recorded, operation time was recorded after operation. Results Compared with T₀, rScO₂ in the three groups was increased significantly at T₁, and decreased significantly at T₃ in group L (P<0.05); compared with T₂, rScO₂ in group L at T₃ was significantly lower (P<0.05); compared with T₃, rScO₂ in group L was increased significantly at T₄ and T₅ (P<0.05). Compared with group N, rScO₂ in group L was decreased significantly at T₃ (P<0.05). Two-factor ANOVA showed that there was no interaction between group and pneumoperitoneum at T₂ and T₃, T₃ and T₄ in the three groups (P>0.05); compared with T₂, rScO₂ at T₃ in group L was significantly lower (P<0.05); compared with T₃,rScO₂ at T₄ in group L was significantly increased (P<0.05). There were no significant differences in SpO₂, HR, MAP, T, pH and Hb among the threes groups at each time point of T₀-T₅. Conclusion Pneumoperitoneum resulted in a significant decrease in rScO₂ on the affected side when PaCO₂ was within 25-29 mmHg during pediatric RALP and the risk of the cerebral oxygen supply-demand unbalance increased.