A driving circuit of a fan includes a magnetic pole sensor for generating a magnetic pole sensing signal, a first waveform generator coupled to the magnetic pole sensor for generating a first waveform according to the magnetic pole sensing signal, a second waveform generator for generating a second waveform, a comparison circuit coupled to the first waveform generator and the second waveform generator for comparing the first waveform and the second waveform for generating a third waveform, a control signal generator coupled to the comparison circuit for generating a control signal according to the third waveform and an external signal, and a current generator coupled to the magnetic pole sensor and the control signal generator for outputting current to a coil of a stator of the fan according to the magnetic pole sensing signal and the control signal.