AIM: This study aims to investigate the predictive value of bedside ultrasound evaluation of venous excess ultrasound grading system (VExUS) for acute kidney injury (AKI) in children after cardiac surgery. METHODS: This retrospective study included 122 pediatric patients who underwent cardiac surgery at the West China Second University Hospital of Sichuan University between January 2024 and November 2024. Based on the occurrence of AKI, patients were divided into the AKI (n = 42) and non-AKI (n = 80) groups. Univariate and binary logistics regression analyses were performed to identify factors influencing AKI. The predictive value of the VExUS grading system for AKI in children after pediatric cardiac surgery was evaluated using receiver operating characteristic (ROC) curve analysis. RESULTS: There were no statistically significant differences (p > 0.05) between the two groups regarding age, gender, Body Mass Index (BMI), length of hospital stay, intraoperative blood loss, postoperative hypotension, 24-hour postoperative urine output, aortic cross-clamp time, preoperative left ventricular ejection fraction, postoperative inadequate circulating blood volume, and preoperative use of positive inotropic drugs, operation time, plasma input, congenital heart disease, radical operation, and emergency surgery. However, statistically significant differences were found in postoperative blood glucose levels, VExUS scores, cardiopulmonary bypass duration, and cyanosis (p < 0.05). Binary logistics regression analysis revealed that blood glucose levels, VExUS, and cyanosis were significant factors influencing AKI after pediatric cardiac surgery (p < 0.05). ROC analysis showed that the area under the curve (AUC) of 0.803 for VExUS, with a standard error of 0.043 (95% confidence interval (CI): 0.719–0.887), a Youden index of 0.48, sensitivity of 76.25%, and specificity of 71.43%. CONCLUSIONS: The VExUS grading system demonstrates significant clinical utility in predicting AKI in children undergoing cardiac surgery.