Abstract: Switch mode power supply is a good selection for UAV. The forward converter will generate transient voltage spikes when the power is switched off and cause wide-band electromagnetic interference with a continuous spectrum. The higher level of the resonant reset will destroy the metal-oxidesemicondutor field-effect transistor(MOSFET). This paper analyzes the magnetic field of the forward converter transformer,explains the reasons in forming voltage spike of the MOSFET,designs a RC branch in parallel to the magnet,and presents a way to select the parameters of the component. To guarantee the long-term operation of the switch,the resistor,capacitor,and diode(RCD) resonant reset circuit is designed. The experimental results agree well with the analysis conclusions.