Background: The incidence of acute myocardial infarction is increasing annually. The primary percutaneous coronary intervention (PCI) is an effective method for treating acute myocardial infarction. However, the no-reflow phenomenon (NRP) during or after PCI can significantly weaken the efficacy of PCI. Therefore, this study aimed to develop and evaluate a predictive nomogram for slow-flow/no-reflow phenomenon (SFP/NRP) in patients with ST-segment elevation myocardial infarction (STEMI).Method: A retrospective observational study was conducted in Heping Hospital and Heji Hospital, affiliated with Changzhi Medical College. A credible random split-sample method was used to divide data into training and validation datasets (split ratio = 0.7:0.3). The outcome variable was SFP/NRP. Least absolute shrinkage and selection operator (LASSO) logistic regression was applied to select predictors and develop the nomogram. The platelet/lymphocyte ratio (PLR), CHA2DS2-VASc score, and HAKTT score are selected as predictors. The discrimination of the nomogram was assessed using the receiver operating characteristic (ROC) curve, and the calibration curve was used to evaluate the accuracy of the prediction. The clinical usefulness of the nomogram was evaluated with decision curve analysis (DCA).Result: The patients (n = 311) with STEMI who underwent emergency PCI from July 2021 to September 2022, were retrospectively analyzed. The incidence of SFP/NRP was found to be 32.5%. The PLR (Odds Ratio (OR): 1.006, 95% Confidence Interval (CI): 1.003-1.010, p = 0.001), CHA2DAS2-VASc score (OR: 1.388, 95% CI: 1.146-1.682, p = 0.001), and HAKTT score (OR: 1.170, 95% CI: 1.100-1.246, p < 0.001) were identified as predictors and developed a nomogram. The nomogram showed good discrimination in both the training (area under the ROC curve (AUC): 0.78, 95% CI: 0.73-0.85) and validation (AUC: 0.70, 95% CI: 0.55-0.84) datasets as well as calibrated in both datasets (allp > 0.05). Moreover, DCA demonstrated that the nomogram is clinically useful.Conclusions: This study proposed an effective nomogram comprising PLR, CHA2DS2-VASc score, and HAKTT score with potential application in facilitating the individualized prediction for SFP/NRP in STEMI patients.