The high frequency core loss is effected by the exciting voltage waveform and the magnetizing current condition. Because the large load current introduces a heavy ringing phenomenon in switches, measuring the high frequency core loss of transformer based on the traditional full-bridge switching mode power converter is limited. In this paper, we propose a new control method for high frequency core loss measurement with full-bridge excitation waveform. Its principle is to offer a path for the magnetizing current to keep its value constant during the free-wheeling period. By doing this, the constant magnetizing current acts as a current source and charges the parasitical capacitance in switches linearly during dead time, the zero voltage switching condition is achieved. As a result, the ringing phenomenon in switches can be significantly reduced, and the accurate measurement for core loss can be achieved for full-bridge power converters.