Objective: To explore the correlation between allogeneic red blood cell (RBC) transfusion and healthcare-associated infections (HAIs) in patients undergoing coronary artery bypass grafting (CABG) during the perioperative period. Methods: A single-center retrospective cohort of 1,170 patients undergoing isolated CABG was analyzed. Multivariable logistic regression and restricted cubic splines (RCS) were employed to explore the nonlinear association between perioperative RBC transfusion (from intraoperative period to 72 hours postoperatively) and HAIs. Results: Among the 1,170 CABG patients, 109 patients (9.2%) received RBC transfusion during the operation or within 3 days after the operation. The risk of HAIs in those who received ≥4 units of RBCs during and within 3 days after the operation was 6.89 times higher than that in the non-transfusion group (95% CI: 3.65-17.20). Furthermore, there was a nonlinear threshold effect between the blood transfusion volume and postoperative HAIs (inflection point: 7.8 units). When the transfusion volume was ≤7.8 units, the risk of HAIs increased by 61% for each additional unit transfused (OR=1.61, 95% CI: 1.21-2.15). Beyond this threshold, no statistically significant association was observed (P=0.289). Conclusion: Perioperative RBC transfusion in CABG patients is associated with an increased incidence of HAIs. The perioperative blood transfusion volume has a curvilinear relationship with the risk of postoperative HAIs. When the blood transfusion volume is ≤7.8 units, the blood transfusion volume has a dose-dependent relationship with postoperative infection, with higher blood transfusion volumes correlating with greater postoperative infection risk. When the blood transfusion volume is >7.8 units, the relationship between the two is not statistically significant. The preventive effect of reducing RBC transfusion on HAIs requires further validation in the future.