A control method is used in a power factor corrector. Firstly, a current command signal from a computing circuit is received. Then, the current command signal is compared with an input signal of the power conversion circuit, so that a current error signal is generated. If the power factor corrector is operated in a transition interval between the first mode and the second mode, an addition operation is performed on the unadjusted current error signal, a feedforward signal and the adjusted current error signal, thereby generating a current control signal. A switch control signal is generated according to the current control signal. A switching element of a power conversion circuit is controlled according to the switch control signal. Consequently, the harmonic distortion of the input current is inhibited.