A multi-phase signal generator and a multi-phase signal generating method thereof. The multi-phase signal generator includes a signal generator, a first comparator, a second comparator and a logic operation circuit. The signal generator generates a periodic signal. The first comparator receives the periodic signal and respectively compares the periodic signal with a first reference voltage and a second reference voltage to generate a first output signal. The second comparator receives the periodic signal and compares the periodic signal with a first threshold voltage to generate a second output signal. The logic operation circuit performs logic operations on the first output signal and the second output signal so as to generate a plurality of first phase output signals.