Objective　To explore the pathogenesis, diagnosis and radiofrequency ablation effect of preexcitation cardiomyopathy in children. Method　The clinical data of a preexcitation cardiomyopathy in a child was analyzed retrospectively. Results　In a 12-year-old boy, electrocardiogram showed type B Wolff-Parkinson-White syndrome. Echocardiography showed dilated cardiomyopathy without tachycardia attack during the course of the disease. Electrophysiological examination revealed right posterior septal accessory pathway. After radiofrequency ablation, electrocardiogram showed that the delta wave disappeared and echocardiography showed that the left ventricle size shrank and the cardiac function improved and the clinical symptoms were significantly improved. Conclusion　The non-synchronization of excitation-mechanical contraction coupling in left ventricle caused by ventricular preexcitation may be the most important pathogenesis of preexcitation cardiomyopathy, in which the overt accessory pathway in the right septum is the most common. Radiofrequency ablation is effective and has a good prognosis.