The present invention provides a control method of a power electronic transformer. The control method of the power electronic transformer is suitable for a power electronic transformer which employs adual active bridge series resonance DC-DC converter. When a high-voltage alternating current side is operated in high power, the working frequency of a switching device in a cascaded H-bridge circuitis regulated according to the current condition to reduce the switching loss. When a DC-DC link is in a high-power transmission working condition, a switching device in a full-bridge circuit, as a receiving end, of the DC-DC converter is locked to reduce the switching loss. Finally, the whole operation efficiency is improved on the premise without influencing the electrical properties of the power electronic transformer.