A multi-phase motor control method controls a multi-phase motor which includes multiple nodes respectively receiving a corresponding number of driving voltage signals to control a rotation of a rotor. The motor control method includes: sensing a signal phase of a current signal corresponding to at least one node, for example by sensing a zero-crossing point of the current signal; determining a reference phase for the current signal; calculating a phase difference between the signal phase and the reference phase; and controlling a phase switching frequency of the stator according to the phase difference, such that the signal phase is close to or in phase with the reference phase, to thereby obtain an optimum rotation speed of the rotor corresponding to a given driving voltage. The present invention also provides a multi-phase motor control device using the motor control method.