Objective To investigate the incidence of cerebral oxygen desaturation events (CDEs) and its related risk factors in infants under 1 year old with congenital heart disease (CHD) after surgery. Methods The clinical data of infants under 1 year old with CHD who underwent cardiopulmonary bypass surgery between January and June 2023 were retrospectively analyzed. According to whether CDEs occurred after surgery, the patients were divided into CDEs group and non-CDEs group. The clinical characteristics of the two groups were compared, and the influencing factors related to CDEs occurrence were analyzed. Results Among 397 infants who underwent CHD surgery, 67 infants (16.9%) developed CDEs after surgery, including 39 boys and 28 girls, with a median age of 4.0 (3.1-5.6) months. There were 330 patients (83.1%) without CDEs, 177 boys and 153 girls, with a median age of 4.5 (3.2-7.7) months. Binary logistic regression analysis showed that higher postoperative pulse oxygen saturation (SpO₂) and higher intraoperative hematocrit (Hct) were independent protective factors for CDEs, while prolonged cardiopulmonary bypass time and moderate to deep hypothermic circulatory arrest were independent risk factors for CDEs (P<0.05). ROC curve analysis showed that postoperative SpO₂, intraoperative Hct, and cardiopulmonary bypass time all had certain predictive value for the occurrence of CDEs (AUC>0.6, P<0.05). Conclusions The incidence of postoperative CDEs in CHD infants under 1 year old is higher. Postoperative SpO₂, intraoperative Hct, duration of cardiopulmonary bypass and cardiopulmonary bypass regimen may predict the incidence of postoperative CDEs in CHD patients in this age group.