Compared with the conventional substation, power electronic substation can not only transform voltage, but also control power and offer power electronic AC and DC interfaces. Therefore, power electronic substation is applied to a demonstration project of distribution network. Its reliability level of power supply is a key concern. Based on the understanding of the principle of Power Electronic Transformer (PET) and the composition of power electronic substation and its main connection scheme, the operation modes of distribution network are analyzed. The reliability analysis model of power electronic substation distribution network is constructed by adopting the fault tree analysis method. The crucial reliability index, such as annual failure rate and annual failure time of the distribution network, is obtained by the minimum cut set. Finally, by means of analyzing and calculating the data collected from demonstration power electronic substation project, it is found that the reliability index of distribution network with power electronic substation is slightly lower than that of the conventional substation. This work is supported by Major Science and Technology Project of State Grid Corporation of China (No. 5205A016002) and Major Fund “Advanced Rail Traffic” of National Key Research and Development Program of China (No. 2017YFB1201000).