Objective To analyze the correlation between levels of serum procalcitonin (PCT), neutrophil-to-lymphocyte ratio (NLR) and C-reactive protein (CRP) and severity of acute pancreatitis (AP). Methods 108 AP patients were selected as AP group, and were divided into mild group (n=51), moderate group (n=36) and severe group (n=21), according to the multiple organ dysfunction score (Marshall score). Another 30 healthy people who had physical examination at the same time were selected as control group. The levels of serum PCT, NLR and CRP were detected in each group, and their correlation with disease severity was analyzed. The receiver operating characteristic curve (ROC) was used to analyze the diagnostic value of serum PCT, NLR and CRP on AP. Results The levels of serum PCT, NLR and CRP in AP group were significantly higher than those in control group (P＜0.05). As disease severity of AP patients worsened, the levels of serum PCT, NLR and CRP were gradually increased, and the differences between the groups were statistically significant (P＜0.05). Correlation analysis showed that serum PCT (r=0.551 P＜0.001), NLR (r=0.785, P＜0.001) and CRP (r=0.538, P＜0.001) in patients with AP had a significant positive correlation with the Marshall score. The AUC values of serum PCT, NLR and CRP in the diagnosis of AP were 0.911 (95% CI: 0.832-0.989), 0.840 (95% CI: 0.756~0.923) and 0.861 (95% CI: 0.762~0.960). With PCT＞1.27 ng/mL, NLR＞4.38 and CRP＞11.57mg/L as the optimal cutoff value, the sensitivities of the three diagnosis were 77.78%, 87.96% and 62.04%, and the specificities were 90.00%, 70.00% and 80.00%, and the sensitivity (96.30%) of the combined diagnosis of the three was higher than that of each index (P＜0.05). Conclusion Serum PCT, NLR and CRP levels are closely related to the occurrence and severity of AP. The three have certain value in the diagnosis and evaluation of AP.