The faults at the ports of star common DC bus multi-port power electronic transformer (SBM-PET) are independent from each other and thus the SBM-PET has the characteristics of multiple operation state, but there is no mathematical analytical model that can effectively characterize its multi-state reliability. A SBM-PET multi-state reliability model is proposed and applied to the reliability evaluation of AC/DC distribution network. Firstly, the structure and working principle of SBM-PET are analyzed. The functional modules are divided according to the characteristics and fault influence range of each component module of SBM-PET. On this basis, considering the redundant configuration of components, the reliability model of each functional module of SBM-PET is established. Then, according to the outage of each functional module of SBM-PET, the multi-state reliability model of SBM-PET is established based on Markov process, the reliability indexes of probability, frequency and average duration time under different states of SBM-PET are solved, and the reliability evaluation model of AC/DC distribution network is established based on the solutions. Finally, the multi-state reliability of SBM-PET and the reliability of AC/DC distribution network are calculated by cases analysis, and the results verify the effectiveness of the proposed model.