Aim To investigate the relationship between neutrophil/lymphocyte ratio (NLR) and the blood flow status of infarct related artery (IRA) in patients with acute myocardial infarction (AMI) before and after primary percutaneous coronary intervention (PPCI). Methods 598 patients with AMI (including STEMI and NSTEMI) treated with PPCI were divided into three groups according to the blood flow status of IRA before and after PPCI:group A:the blood flow of IRA before PPCI was TIMI Ⅲ grade; group B:the blood flow of IRA was TIMI 0～Ⅱ grade before PPCI, and TIMI Ⅲ grade after PPCI; group C:the blood flow of IRA was TIMI 0～Ⅱ grade before PPCI and after PPCI. At the same time, NLR and related clinical parameters were detected and Logistic regression analysis was performed. Results There were significant differences in high sensitivity C-reactive protein (hs-CRP), NLR, cardiac troponin T(cTnT) and left ventricular ejection fraction (LVEF) among the three groups. In group A, the values of hs-CRP, NLR and cTnT were the lowest, and LVEF was the highest. In group C, the values of hs-CRP, NLR and cTnT were the highest, while LVEF was the lowest, and the Killip classification≥2 was more common. The mortality was the highest in group C. Multivariate Logistic regression analysis showed that NLR was independently correlated with the blood flow status of IRA, high NLR predicted a higher incidence of TIMI 0～Ⅱ grade in IRA blood flow before and after PPCI. Conclusions NLR is a strong and independent predictor of blood flow status of IRA. High NLR indicates a worse prognosis in AMI patients, which is useful for early risk stratification in patients with AMI undergoing PPCI.