A multi-step charge pump having a power input terminal and a power output terminal is provided. The multi-step charge pump includes a plurality of capacitors, wherein each of the capacitors has a capacitance. A plurality of switching devices is connected among the capacitors, the power input terminal and the power output terminal. A switch-controlling unit controls the on/off states of the switches, wherein a charging-phase circuit corresponding to a pumping level is formed to charge the capacitors and an output-phase circuit is formed to output a voltage from the power output terminal. At least one of the capacitors herein is changeably selected as a voltage-regulating capacitor.