Objective To Provide clinical references for explaining atrial fibrillation maintaining mechanism,by analyzing the f wave and left atrial inner dimension in patients with atrial fibrillation.Methods A total of 391 cases of atrial fibrillation was collected from January 2008 to January 2011 in our hospital,then 50 cases were selected randomly from chronic atrial fibrillation and 50 cases from paroxysmal atrial fibrillation.The amplitude of f wave,timing,f-f interval and left atrial dimension,and so on,were measured,then made a statistics analysis of the results.Results The index above in the Paroxysmal atrial fibrillation group are lower than that of the persistent atrial fibrillation,except inner diameter.There were statistic differences between the two groups(P0.05).Conclusion The increase of left atrial dimension,the shorten of refractory period of atrium maybe the pathological mechanism of atrial fibrillation.