A frequency locking method, for locking an output signal outputted from a frequency locking circuit to a target frequency, comprising: (a) detecting an output frequency of the output signal, wherein the output signal is generated according to an oscillating frequency of a controllable oscillator; (b) computing a frequency difference between the output frequency and the target frequency; (c) utilizing a controllable factor adjusting device to provide and to adjust a normalization factor according to the frequency difference, to anticipate a gain of the controllable oscillator and to provide a control signal related with the normalization factor and the frequency difference, wherein the output frequency is related with a product of the normalization factor and the gain of the controllable oscillator; and (d) controlling the controllable oscillator according to the control signal, such that the output frequency approaches to the target frequency.