A switching power conversion apparatus includes: a multi-level power stage, a PWM control circuit, a multi-level driver circuit, a bootstrap capacitor control circuit and a driving power control circuit. The bootstrap capacitor control circuit includes bootstrap capacitor control switches. During a charging period, a bootstrap control signal controls the bootstrap capacitor control switches, to electrically connect a second bootstrap node to the ground voltage level, whereby the supply voltage charges the bootstrap capacitor via the bootstrap diode. During a pumping period, the bootstrap control signal controls the bootstrap capacitor control switches to electrically connect the second bootstrap node to one of the upper-gate nodes or the switching node, whereby the voltage of the first bootstrap node is pumped to a corresponding pumping voltage level.