Objective: To retrospectively analyze the risk factors for postoperative delirium in patients after major open abdominal surgery and to explore the predictive value of Surgical Apgar Score (SAS) for postoperative delirium. Methods: We retrospectively collected preoperative and intraoperative clinical data from 320 patients who had undergone major open abdominal surgery between January 2015 and December 2016 in our hospital, and calculated the SAS. SAS was calculated based on the lowest mean arterial pressure (MAP), lowest heart rate (HR) and estimated blood loss in surgery. The patients were assigned into two groups, a delirium group and a non-delirium group, depending on whether postoperative delirium developed or not. Different variables between the two groups were selected, and multi-variate Logistic regression analysis was employed to detect the independent risk factors for postoperative delirium. The area under the curve (AUC) from the receiver operating characteristic curve (ROC) was used to detect the SAS’s discriminatory power for postoperative delirium. The optimal cut-off value and corresponding sensitivity and specificity were also calculated. Results: Postoperative delirium occurred in 128 patients of 320 patients, with an incidence rate of 40%. The multi-variate Logistic regression analysis showed that ages over 65 years [P=0.013, adjusted OR (odds ratio)=1.972], preoperative coagulation dysfunction (P=0.002, adjusted OR=2.425), diabetes (P=0.030, adjusted OR=2.128) were independent risk factors for postoperative delirium. The risk of delirium was decreased as the SAS increased (P<0.001, adjusted OR=0.754). After the surgery, the area under curve was 0.648 (95% confidence interval, 0.587~0.709), and the optimal cut-off was 6 with a sensitivity of 76.0% and a specificity of 71.1%, according to the prediction of SAS scores. Conclusion: Surgical Apgar score ≤6 has a limited predicting power for postoperative delirium in patients undergoing open abdominal surgery.