Objective To explore and develop a new type of risk scale for assessment of critically ill patients at the end of operation, so as to provide guidance for admission in intensive care unit (ICU) after surgery. Methods Retrospective analysis was performed where clinical data were collected from patients who were admitted in three Grade‑A‑Tertiary hospitals for abdominal surgery before entry into ICU. The patients were divided into two groups: group A and group B. Patients in group A received organ function support and close monitoring in ICU after operation, and were considered necessary to stay in ICU. Those in group B did not receive organ function support or close monitoring in ICU, and were considered unnecessary to stay in ICU. A self‑made postoperative risk scale was used to evaluate the patients, and their scores and 95% confidence interval (CI) were obtained. The postoperative risk score which was ≥ the lower limit of 95%CI in group A was set as the criteria for admission to ICU, while the postoperative risk score which was ≤ the lower limit of 95%CI in group B were set as the criteria for returning to the ward. The error rate of patients in group A and group B was calculated. Acute Physiology and Chronic Health Evaluation Ⅱ (APACHEⅡ) was used as a control to evaluate the postoperative risk score and the receiver operating characteristic (ROC) curve was plotted to evaluate the accuracy of the risk score in predicting admission to ICU or returning to ward. Results There were 202 patients in group A and 322 patients in group B. There was no significant difference in the risk scores among patients in the three hospitals (P>0.05). The risk score was 16.87±4.02 (95%CI 16.22‒17.48) for group B and 24.57±6.23 (95%CI 23.32‒25.75) for group A. There was significant difference in the risk scores between two groups (P<0.05). The error rate was 3% for group A and 6% for group B. The area under ROC curve was 0.866 (95%CI 0.818‒0.914), with a sensitivity of 0.755 and a specificity of 0.830. Conclusions The postoperative risk scale is useful to predict the necessity of ICU stay. Patients with ≥23 scores are strongly recommended for ICU stay. Those with ≤16 scores are suggested not to stay in ICU. If the score ranges from 17 to 22, the patients are suggested to admit into post‑anesthesia care unit (PACU) or receive therapeutic regimens suggested by anesthesiologists and surgeons based on their other clinical conditions.