Objective To investigate the risk factors of new-onset postoperative atrial fibrillation (POAF) in patients who underwent isolated off-pump coronary artery bypass grafting (OPCAB). Methods Between January 2016 and January 2018, a total of 583 patients who underwent OPCAB in TEDA International Cardiovascular Hospital were retrospectively analyzed. There were 434 males and 149 females with an average age of 62.79±8.08 years. The patients were divided into 2 groups, a POAF group (n=158) and a non-POAF group (n=425) , in accordance with the occurrence of POAF. The perioperative clinical parameters of the two groups were analyzed by univariate analysis. Then, statistically significant factors in the univariate analysis were subjected to multivariate logistic regression analysis to determine if it was an independent risk factor for POAF. Results Univariate analysis showed that age≥65 years (P=0.012), history of chronic obstructive pulmonary disease (COPD, P=0.028), left atrial diameter (LAD)≥38 mm (P=0.016) and neutrophil-lymphocyte ratio (NLR, P=0.002) were related to POAF. Logistic multivariate regression analysis showed that age≥65 years (OR=1.717, P=0.006), LAD≥38 mm (OR=1.562, P=0.023) and higher NLR level (OR=1.215, P=0.022) were the independent risk factors of POAF after OPCAB, but not previous history of COPD (OR=2.489, P=0.326). Conclusion In patients with OPCAB, advanced age (≥65 years), LAD enlargement (≥38 mm) and higher NLR level are the independent risk factors of POAF after OPCAB.