A resonant converter includes: an input power supply, a bleeder circuit, a multi-level switching network, a resonant unit, and a transformer. The input power supply is connected to the bleeder circuit, the multi-level switching network is connected to the bleeder circuit, a clamping middle point of the multi-level switching network is connected to a middle point of the bleeder circuit; one end of the resonant unit is connected to the output terminal of the multi-level switching network, and the other end of the resonant unit is connected to one end of a primary side of the transformer; and the multi-level switching network instructs the output terminal of the multi-level switching network to output a square wave voltage with different amplitudes, to serve as an input voltage of the resonant unit, where the input voltage is used to adjust a gain of the resonant converter.