A power converting device includes a switching unit, a resonant unit, a converting unit, a rectifying and filtering unit, an inductance-sensing unit, and a driver. The resonant unit is electrically connected to the switching unit and includes a resonant capacitor, a resonant inductor, and a variable magnetizing-inductor having at least two inductances, the resonant inductor is electrically connected to the resonant capacitor and the variable magnetizing-inductor. The converting unit is electrically connected to the resonant unit. The rectifying and filtering unit is electrically connected to the converting unit. The inductance-sensing unit is electrically connected to the rectifying and filtering unit, the inductance-sensing unit instantaneously senses inductances of the variable magnetizing-inductor. The driver is electrically connected to the inductance-sensing unit and the switching unit, the driver is configured for controlling a switching frequency of the switching unit according to an inductance instantaneously sensed by the inductance-sensing unit.