Objective To investigate the values of systemic inflammatory response index （SIRI）， systemic immunoinflammatory index （SII）， neutrophil count/lymphocyte count （NLR）， platelet count/lymphocyte count （PLR） and lymphocyte count/monocyte count （LMR） in prediction of the severity of acute pancreatitis （AP） at early stage. Methods The clinical data on 666 AP patients admitted to the department of hepatobiliary surgery， the First Affiliated Hospital of Anhui University of Science and Technology， from January 2020 to November 2023 were retrospectively analyzed. The patients were divided into a mild group （MAP group， mild acute pancreatitis） and a non-mild group （non-MAP group， including moderate to severe acute pancreatitis）. Blood routine and biochemical indicators were collected at admission and 24 hours after admission. The differences in SIRI， SII， NLR， PLR and LMR between the two groups were compared， so were the values of these five indexes in prediction of non-MAP. Results Of the 666 AP patients， 507 were in the MAP group and 159 in the non-MAP group. In the non-MAP group， C-reactive protein （CRP）， SIRI， SII， and NLR were higher than those in the MAP group 24 hours after admission， while LMR was lower than that in the MAP group， and the differences were statistically significant （P < 0.05）. CRP （HR = 1.008， 95%CI： 1.004 ~ 1.012， P < 0.05） and SIRI （HR = 1.216， 95%CI： 1.029 ~ 1.436， P < 0.05） were identified as the risk factors for the severity of AP. The ROC curve showed that the AUC and sensitivity of SIRI for predicting non-MAP 24 hours after admission were 0.718 and 75.00%， respectively， higher than those of SII， CRP， NLR， and LMR. Both SIRI and CRP had AUC values greater than 0.7， and the combined AUC was 0.788 （0.738 ~ 0.837）， the sensitivity was 86.00% and the specificity was 81.44%. Conclusions SIRI can be used as a predictor of disease severity in early AP patients， and combined with CRP can improve the predictive value.