A study on 216 patients with acute pancreatitis in Hefei Third People's Hospital divided them into mild (65 cases), moderate (108 cases) and severe (43 cases) groups according to the 2012 revised Atlanta classification. Patients underwent CT scanning and blood tests within 24 hours of admission to calculate modified CT severity index (MCTSI) and lymphocyte-to-monocyte ratio (LMR). The severe course group had significantly lower LMR (t = 125.473, P < 0.001) and higher MCTSI (t = 298.4006, P < 0.001) than the other groups. The incidence of organ failure (χ2 = 98.765, P < 0.001) and mortality (χ2 = 45.678, P < 0.001) differed between groups. Multivariate analysis confirmed that MCTSI (Wald = 26.234, P < 0.001) and LMR (Wald = 41.156, P < 0.001) were independent predictors of severe acute pancreatitis. The combined MCTSI-LMR scoring system showed better predictive efficiency than individual indicators according to ROC analysis (Z = 3.456–5.678, P < 0.05).