Power Electronic Transformer (PET) has potential application value in distribution network. This paper presents a novel PET with only one stage single-phase to single-phase AC/AC converter at the primary side of the transformer, the high voltage end, which generates high-frequency alternating voltage. The secondary side of the transformer, the low voltage end, is also one stage AC/AC converter, by which low power frequency voltage can be created. The final stage is a resistive converter obtaining low DC output voltage and unitary input power factor. Consequently, the unitary power factor can be reflected to the mains side and the PET owns a four-quadrant operation capability. The theory of four-quadrant PET is analyzed and the simulation analysis using MATLAB/SIMULINK is also provided. The result shows that this kind of PET holds some prominent advantages such as simple structure, easy to control, safe commutation, unitary input power factor, bidirectional power flow and easy to cascade. So it has application value.