To explore the value of red cell distribution width to serum calcium ratio combined BISAP scores in assessment of the severity of acute pancreatitis (AP). Methods This retrospective research analyzed 132 patients with AP treated in our department from June, 2018 to June, 2019. According to the severity, the patients were classified into severe acute pancreatitis (SAP) group and mild or moderately severe acute pancreatitis (non-SAP) group. The demographic data was analyzed. Results The RCR of patients in the SAP group was significantly higher on the 1st, 3rd and 7th days after hospitalization than in the non-SAP group, at the same time, non-SAP group, SAP group, RCR is at the highest level on the first day, followed by the gradual decrease in hospital stay, more statistically significant (P＜0.05). The results of the ROC curve show that the area under the curve (AUC) of the BISAP score is 0.848, the RCR is 0.744, RDW (ROC:0.695), Ca2+(ROC:0.650), and the AUC (0.883) of the RCR combined BISAP score is the highest, with sensitivity of 79.31% and specialty of 91.26%. Conclusion RCR can be used as an indicator to predict AP severity, combined with BISAP score, to predict AP severity more accurately