Abstract: Objective To investigate the value of preoperative fragmented QRS (fQRS) in prediction of the prognosis of patients with acute ST-segment elevation myocardial infarction (STEMI) undergoing emergency percutaneous coronary intervention (PCI). Methods A total of 100 patients with STEMI who underwent electrocardiogram (ECG) examination and emergency PCI in the hospital from April 2013 to May 2017 were enrolled in the study. Routine 12-lead dynamic ECG detection was performed before surgery and at 2 hours after surgery. According to the presence of fQRS on preoperative ECG, the patients were divided into fQRS group (42 cases) and nfQRS group (58 cases). The clinical data, laboratory parameters and ECG indicators were compared between the two groups. All patients were followed up for at least 1 year. The incidence of major adverse cardiac events (MACE) was recorded and statistical analysis was performed with occurrence of MACE as poor prognosis. Results Compared with the nfQRS group, the peaks of troponin (cTnI) and creatine kinase isoenzyme (CK-MB) were significantly higher in fQRS group. The preoperative QRS interval was significantly longer, the postoperative ST segment elevation was significantly greater, and ST segment drop rate was significantly lower (P<0.05). The incidence of MACE in fQRS group during 1-year follow-up after PCI was significantly higher than that in nfQRS group (40.48% vs. 13.79%), and the MACE free survival curve of fQRS group was lower than that of nfQRS group (P<0.05). Cox risk regression analysis showed that preoperative QRS interval, postoperative ST segment elevation, postoperative ST segment drop rate and fQRS were independent risk factors for poor prognosis (P<0.05). Conclusion The presence of fQRS before emergency PCI may indicate that patients with STEMI are seriously ill, which is closely related to postoperative MACE and can be used to predict the prognosis of patients.