The cascaded multiport Power Electronic Transformer (PET) is a key equipment for future distribution grid with multi-voltage level and AC/DC hybrid feature, whose reliability has significant effect on the distribution grid reliability level. First, the typical topological structure and working principle of cascaded multiport PET are analyzed. Secondly, the reliability evaluation model for PET considering the device redundancy is established based on the engineering reliability theory. Then the effect of cascaded multiport PET on the AC/DC hybrid distribution network reliability is analyzed. Finally, the case studies are provided with a ‘hand in hand’ AC/DC hybrid power distribution network structure. The PET reliability levels under different design patterns and the redundancy levels are calculated. The influence of PET on reliability of AC/DC hybrid distribution system and its sensitivity analysis are carried out, which verifies the correctness and validity of the proposed algorithm. This work is supported by Science and Technology Project of China Southern Power Grid Co., Ltd. (No. GDKJQQ20161200).