Abstract: The power electronic transformer（PET） is one of the key devices in the flexible DC distribution system. Due to the small simulation step size caused by high-frequency characteristics of PET, the detailed electromagnetic transient（EMT）simulation of PET is extremely time-consuming, especially for the multi-active-bridge（MAB） based PET. Hence the simulation speed needs to be accelerated. This paper proposes a simplified EMT equivalent model of the cascaded H-bridge（CHB） type MABbased PET. The structural characteristics of MAB are analyzed. For the CHB slow-change circuit, the switching function model is adopted to divide the circuit states. Based on the generalized state-space average method,for the fast-changing circuit of MAB, the equivalent that the Fourier decomposition method is used and the harmonic characteristics of key orders are kept is achieved. The processing methods of port electrical variables in different cascading modes are proposed to improve the simulation acceleration ratio while preserving accuracy. The detailed model and the simplified equivalent model of input-series output-parallel type MABbased PET are built in PSCAD/EMTDC. The simulation results show that the simplified EMT equivalent model has similar accuracy and higher efficiency compared with the detailed model.