A frequency divider and a control method thereof are provided. The frequency divider includes a phase selector and a control circuit. The phase selector receives N input signals, and selects a first input signal from the N input signals as an output signal according to N selection signals. The frequency of the N input signals are the same, and the phase of the N input signals are different, and every adjacent two of the N input signals have a phase difference of 360°/N, wherein N is a positive integer larger than 2. The control circuit updates the N selection signals according to the output signal, such that the phase selector switches the output signal from the first input signal to a second input signal of the N input signals, wherein the phase of the second input signal leads the phase of the first input signal by 360°/N.