An optical signal processing method, comprising: separately quantizing (SI03), by a coherent receiver, an in-phase signal I and a quadrature signal Q; and after combining (S104) the quantized signals into a complex signal, performing (SI05), by the coherent receiver, digital signal processing on the complex signal, characterized in that a procedure of obtaining (S102) the in-phase signal I comprises: calculating (S201), by the coherent receiver, a sum of a received in-phase analog signal XI in a first polarization direction and a received in-phase analog signal YI in a second polarization direction; and if the sum of the XI and the YI is less than a preset value (S202), obtaining the in-phase signal I by calculating (S204) a sum of a first phase-inverted analog signal and the XI or the YI whichever has a larger amplitude, wherein the first phase-inverted analog signal is a signal obtained by performing phase-inversion processing on the XI or the YI whichever has a smaller amplitude (S203); and a procedure of obtaining (SI02) the quadrature signal Q comprises: calculating, by the coherent receiver, a sum of a received quadrature analog signal XQ in the first polarization direction and a received quadrature analog signal YQ in the second polarization direction; and if the sum of the XQ and the YQ is less than a preset value, obtaining the quadrature signal Q by calculating a sum of a second phase-inverted analog signal and the XQ or the YQ whichever has a larger amplitude, wherein the second phase-inverted analog signal is a signal obtained by performing phase-inversion processing on the XQ or the YQ whichever has a smaller amplitude. separately quantizing (SI03), by a coherent receiver, an in-phase signal I and a quadrature signal Q; and after combining (S104) the quantized signals into a complex signal, performing (SI05), by the coherent receiver, digital signal processing on the complex signal, characterized in that a procedure of obtaining (S102) the in-phase signal I comprises: calculating (S201), by the coherent receiver, a sum of a received in-phase analog signal XI in a first polarization direction and a received in-phase analog signal YI in a second polarization direction; and if the sum of the XI and the YI is less than a preset value (S202), obtaining the in-phase signal I by calculating (S204) a sum of a first phase-inverted analog signal and the XI or the YI whichever has a larger amplitude, wherein the first phase-inverted analog signal is a signal obtained by performing phase-inversion processing on the XI or the YI whichever has a smaller amplitude (S203); and a procedure of obtaining (SI02) the quadrature signal Q comprises: calculating, by the coherent receiver, a sum of a received quadrature analog signal XQ in the first polarization direction and a received quadrature analog signal YQ in the second polarization direction; and if the sum of the XQ and the YQ is less than a preset value, obtaining the quadrature signal Q by calculating a sum of a second phase-inverted analog signal and the XQ or the YQ whichever has a larger amplitude, wherein the second phase-inverted analog signal is a signal obtained by performing phase-inversion processing on the XQ or the YQ whichever has a smaller amplitude. <EOS>