The present application discloses a power converter and a controlling method thereof. The power converter at least comprises an inductor, a parasitic capacitor, an energy storage switch and a free-wheeling switch, and the controlling method is used for enabling the energy storage switch to maintain zero-voltage turn-on during the normal operation of the power converter. The controlling method comprising: within a switching period, the free-wheeling switch is turned on again for a preset time after the free-wheeling switch is turned on and turned off for the first time and after the inductor and the parasitic capacitor resonate, so that a voltage between two terminals of the energy storage switch can decline to zero, and when the voltage between two terminals of the energy storage switch declines to zero, the energy storage switch is turned on, thereby entering the next switching period of the power converter.