Objective:To analyse the clinical feature of atrial fibrillation (AF) with secundum atrial septal defect (ASD) and the outcomes of different treatment methods of AF. Methods:To calculate the incidence of AF in 641 patients with ASD before transcathter closure. And to find the risk factors in the patients with AF. To compare the outcomes between cardioversion of AF with catheter ablation and with antiarrhythmic drug therapy. Result:The incidence of AF was 4.8% in 641 patients with ASD,8.4% in patients above 40 years old and 25% in patients above 60 years old. Compared with the patients without AF,the patients suffering AF were characterized by much more males,higher pressure of right atrium,higher pressure of pulmonary,larger diameter of left atrium,larger left ventricular end diastolic diameter and lower left ventricular ejection fraction. Male,aged above 40 years old and larger diameter of left atrium were identified as risk factors for AF in ASD patients. The rate of cardioversion of AF with catheter ablation was higher than that of antiarrhythmic drug therapy. Conclusion:The incidence of AF was high in patients with ASD. Male,aged above 40 years old and larger diameter of left atrium were identified as risk factors for AF in ASD patients. Catheter ablation of AF should be a effective method for treatment of AF with ASD.