A multi-phase power controller coupled to resonant power converting circuits providing an output voltage is disclosed. The multi-phase power controller includes a current sensing unit, a frequency adjusting circuit and a duty cycle adjusting circuit. The current sensing unit, coupled to a first resonant power converting circuit, provides a first sensing current. The frequency adjusting circuit includes an error amplifier and a first ramp signal generation circuit. The error amplifier provides an error signal according to the output voltage and a reference voltage. The first ramp signal generation circuit provides a first ramp signal according to the error signal. The duty cycle adjusting circuit provides a first PWM signal to the first resonant power converting circuit according to a default voltage and the first ramp signal. The change of the duty cycle of the first PWM signal is related to the first sensing current, the default voltage and the first ramp signal.