The invention discloses an optical phase demodulation method and system based on polarization-division receiving. The method comprises the following methods that I/Q demodulation is carried out on optical signals collected by two sensing points, and signal polarization receiving is carried out by using a polarization receiving device to obtain corresponding signal components; an optical phase vector is constructed according to the corresponding signal components; a birefringence phase vector is determined according to the optical phase vector, and the phase difference is normalized; and afterthe birefringence phase vector is compensated, the phase change between the two sensing points is obtained through vector synthesis. According to the invention, a birefringence phase vector is compensated, so that the influence of polarization fading on signal demodulation is reduced, and the system stability is improved; and the I signal and the Q signal are subjected to orthogonal decomposition,and optical signals are converted into a vector to realize depolarized phase demodulation, so that the birefringence phase difference can be accurately estimated, and the accuracy of signal restoration is improved.