Objective To explore the predictive value of peripheral blood myeloperoxidase (MPO) combined with neutrophil/lymphocyte ratio (NLR) and high-sensitivity C-reactive protein (hs-CRP) for major adverse cardiac events (MACE) after percutaneous coronary artery (PCI) in patients with ST-segment elevation myocardial infarction (STEMI).Methods A total of 178 STEMI patients admitted to our hospital from May 2016 to August 2020 were selected. All patients underwent PCI and were followed up for 1 year. The clinical data were collected, and the levels of MPO, NLR and hs-CRP in peripheral blood were measured before PCI. The degree of coronary artery stenosis of the patients, the levels of MPO, NLR, and hs-CRP in peripheral blood of STEMI patients with different levels of disease severity, the incidence of MACE one year after operation, factors affecting the occurrence of MACE in STEMI patients after PCI, and the value of peripheral blood MPO, NLR, and hs-CRP in predicting the occurrence of MACE in STEMI patients after PCI were analyzed.Results The peripheral blood MPO, NLR and hs-CRP levels in the severe stenosis group were higher than those in the moderate stenosis group and the mild stenosis group (P < 0.05), and they were higher in the moderate stenosis group relative to those in the mild stenosis group (P < 0.05). The multivariable Logistic regression analysis showed that cystatin C (Cys C) [O^R = 3.662 (95% CI: 1.507, 8.899) ], MPO [O^R = 3.725 (95% CI: 1.533, 9.052) ], NLR [O^R = 4.088 (95% CI: 1.682, 9.935) ], hs-CRP [O^R = 5.089 (95% CI: 2.094, 12.367) ] and low-density lipoprotein cholesterol (LDL-C) [O^R = 6.385 (95% CI: 2.627, 15.518) ] were factors affecting the occurrence of MACE after PCI in STEMI patients (P < 0.05). The receiver operating characteristic (ROC) curve analysis showed that area under the ROC curve (AUC) of peripheral blood MPO, NLR, hs-CRP and their combination for predicting the occurrence of MACE in STEMI patients after PCI was 0.749 (95% CI: 0.650, 0.849), 0.758 (95% CI: 0.657, 0.859), 0.775 (95% CI: 0.675, 0.876), and 0.898 (95% CI: 0.835, 0.962), respectively.Conclusions The levels of MPO, NLR and hs-CRP in peripheral blood are related to the disease severity of STEMI patients and the occurrence of MACE after PCI, and the combination of the three well predicts the occurrence of MACE after PCI in STEMI patients.