Aim To explore the characteristics and risk factors of malignant ventricular arrhythmia(MVA)in patients with ST-elevation myocardial infarction(STEMI). Methods 371 patients with STEMI treated with primary percutaneous coronary intervention(PCI) were studied.STEMI patients were divided into MVA group(n=38) and the group without MVA according to whether patients with ventricular fibrillation and sustained ventricular tachycardia before and during primary PCI.Age,gender,history of angina,previous MI,history of hypertension,history of diabetes,history of smoking,Killip class,location of MI,number of vessels,crime vessel,time between onset of symptoms and admission,triglycerides,cholesterol,high density lipoprotein,low density lipoprotein,glycated hemoglobin,fibrinogen,D-dimer,blood urea nitrogen,creatinine,serum potassium,uric acid,blood glucose,leukocyte,neutrophil percentage,and hemoglobin were recorded and compared between MVA group and the group without MVA.The risk factors of MVA were determined by Logistic regression analysis. Results Logistic regression analysis showed the Killip class and creatinine were major risk factors of MVA in patients with STEMI.The highest contribution was Killip class. Conclusion Higher Killip class is a vital determinant of MVA in patients with STEMI before and during primary PCI.