Objective To investigate the occurrence of new-onset postoperative atrial fibrillation (POAF) in intensive care unit (ICU) patients after non-cardiac surgery, and to analyze its risk factors and impact on short-time outcomes. Methods A retrospective nested case-control study was conducted among the 2586 cases who underwent non-cardiac procedures and then admitted into ICU in the period from January 2011 to December 2013. Those with new-onset POAF during hospitalization were screened out. Control patients who were matched in age, gender and location of surgery were selected at a 1∶[KG-*2]2 ratio. SPSS statistics 21.0 was used to perform the statistical analysis. Risk factors were screened with multivariate logistic regression analysis. Early postoperative outcomes were compared between the 2 groups. Results Among the subjects, 2.7%(71/2586) developed new-onset POAF. The incidence was quite higher in those very old (≥75 years old) and in those after intra-thoracic surgery. In the patients who developed new-onset POAF, 77.5%(55/71) occurred within 3 d postoperatively, and only 33.8%(24/71) complained of discomfort. Sepsis (OR=11.81, 95%CI 1.72-81.00, P=0.012), hypokalemia (OR=19.48,5%CI 2.31-164.09, P=0.006), postoperative acute congestive heart failure (OR=9.91, 95%CI 1.92-51.22, P=0.006), and new-onset non-atrial fibrillation arrhythmias (OR=20.32,5%CI 3.51-117.55,P=0.001) were independent risk factors for new-onset POAF in the matched patients. Higher in-hospital mortality was associated with longer mechanical ventilation and ICU stay in these patients. Conclusion The incidence of new-onset POAF is 2.7% in the patients admitted to ICU after non-cardiac surgery. The condition is more common in the very elderly (≥75 years old) and those after intra-thoracic surgery. Sepsis, acute congestive heart failure, hypokalemia and new-onset non-AF arrhythmias are independent risk factors of POAF in the matched patients. New-onset POAF is deteriorated with worse outcomes.