The topologies of input stage, isolation stage and output stage of power electronic transformer were introduced, respectively. Using the type of clamp double sub-module modular multilevel converter which has the function of DC fault blocking, the dual active bridge and three-phase inverter as the research objects, the fault characteristics of the short-circuit and open-circuit fault occurred in the power switches which are included in the input stage, isolation stage and output stage of power electronic transformer were analyzed. Based on PSCAD platform, the simulation model of 10kV power electronic transformer was built. The analyzed fault types of power switches were simulated and verified, which proved the correctness of the theoretical analysis. The fault characteristics of all analyzed faults were statistically obtained according to the simulation results. The fault types which have serious impacts on power electronic trans-former were pointed out.