The invention discloses a differential-mode component extraction method of optical signal, wherein the optical signal comprises a first optical signal and a second optical signal, and the method includes the following steps: obtaining the voltage signals of the first signal and the second signal; then obtaining the first voltage signal and the second voltage signal; obtaining the dispersion of the first voltage signal and the second voltage signal; adjusting the first voltage signal and the second voltage signal according to the dispersion; and obtaining the differential-mode component of thefirst voltage signal and the second voltage signal. The common-mode component of the voltage signal in the two photoelectric paths is extracted firstly; and the micro-controller compares the common-mode component and uses the digital potentiometer to adjust the voltage signal according to the differential value. The differential-mode component of the voltage signal is then obtained according to the differential amplification circuit. Intelligent adjustment can be carried out for the voltage signal on the photoelectric path, and the differential-mode signal is more accurately extracted.