Abstract： Objective To analyze the electrocardiogram feature, differential diagnosis and treatment of pre-excitation syndrome complicating atrial fibrillation. Methods Sixteen patients of pre-excitation syndrome complicat-ed with atrial fibrillation. Results The ventricular rate of 16 patients was 160 to 240 beats per minute and the aver-age rate was 182 beats per minute. Most QRS waves appeared with the different combination of complete pre-excita-tion graph, typical pre-excitation graph and normal QRS waves. Most QRS waves of those patients showed pre-exci-tation graph. The different combination showed typical pre-excitation graph and normal QRS waves and very few showed complete pre-excitation graph. Conclusions The electrocardiogram features of pre-excitation syndrome complicated with atrial fibrillation showes very rapid ventricular rate, absolute inequality of RR interval, widen QRS waves with delta wave. QRS waves showes complete pre-excitation graph and the different combination of typical pre-excitation graph and normal QRS waves. Those complicating first and third degree atrioventricular block of fight way showes complete pre-excitation graph.