The prognostic value of the left atrial function index (LAFI) in acute ST segment elevation myocardial infarction (STEMI) patients treated with percutaneous coronary intervention (PCI) is unknown. This study sought to determine whether the LAFI predicts prognosis in STEMI patients treated with PCI. Patients with newly diagnosed STEMI who were treated with PCI in Hunan Provincial People's Hospital from March 2020 to October 2020 were prospectively enrolled. All patients underwent transthoracic echocardiography at baseline and follow-up. The endpoint events included rehospitalization due to unstable angina, nonfatal myocardial infarction, rehospitalization due to heart failure and cardiovascular death. A total of 156 STEMI patients treated with PCI were studied with a median follow-up of 14 months. Forty-eight patients had endpoint events. The LAFI had the highest area under the receiver operating characteristic curve (AUC) predicting the endpoint events, with an AUC of 0.90 (95% CI 0.84–0.94). Multivariate Cox analysis demonstrated that only the LAFI (HR: 0.91, 95% CI 0.87–0.96,P< 0.0001) was independently predictive of endpoint events. Kaplan‒Meier survival curves showed that patients with an LAFI ≤ 42.25 cm/cc/m2had more events than patients with an LAFI > 42.25 cm/cc/m2(HR: 19.15, 95% CI 8.90–41.21,P< 0.001). The LAFI is a strong and independent predictor of events in STEMI patients treated with PCI.