A quadrature phase shift keying, QPSK, signal conjugate relationship identification method, wherein the method comprises: controlling a QPSK modulator to receive a first binary sequence signal, using the first binary sequence signal to modulate an optical signal to obtain a first signal, and determining, within a first predetermined range, a first bias voltage of a parent MZ modulator in the QPSK modulator, so that the first signal at the first bias voltage is a QPSK signal and a root mean square power of the first signal at the first bias voltage is the smallest (101; 201); controlling the QPSK modulator to receive a second binary sequence signal, using the second binary sequence signal to modulate the optical signal to obtain a second signal, determining a second range within the first predetermined range according to the first bias voltage, and determining, within the second range, a second bias voltage of the parent MZ modulator in the QPSK modulator, so that a root mean square power of the second signal at the second bias voltage is the smallest (102; 202); and determining a conjugate relationship of the QPSK signal according to a relationship between the first bias voltage and the second bias voltage(103; 203); wherein the first binary sequence signal is a pseudo random binary sequence signal, and the second binary sequence signal is formed by periodically inserting a high-frequency sequence into the first binary sequence signal; the first predetermined range is an adjustable range of a Bias voltage of the parent MZ modulator; the second range is V 1 -0.5%*V-V 1 +0.5%*V, where V 1 is the first Bias voltage, and V is a half-wave voltage, where the half-wave voltage is a parameter of the MZ modulator. controlling a QPSK modulator to receive a first binary sequence signal, using the first binary sequence signal to modulate an optical signal to obtain a first signal, and determining, within a first predetermined range, a first bias voltage of a parent MZ modulator in the QPSK modulator, so that the first signal at the first bias voltage is a QPSK signal and a root mean square power of the first signal at the first bias voltage is the smallest (101; 201); controlling the QPSK modulator to receive a second binary sequence signal, using the second binary sequence signal to modulate the optical signal to obtain a second signal, determining a second range within the first predetermined range according to the first bias voltage, and determining, within the second range, a second bias voltage of the parent MZ modulator in the QPSK modulator, so that a root mean square power of the second signal at the second bias voltage is the smallest (102; 202); and determining a conjugate relationship of the QPSK signal according to a relationship between the first bias voltage and the second bias voltage(103; 203); wherein the first binary sequence signal is a pseudo random binary sequence signal, and the second binary sequence signal is formed by periodically inserting a high-frequency sequence into the first binary sequence signal; the first predetermined range is an adjustable range of a Bias voltage of the parent MZ modulator; the second range is V 1 -0.5%*V-V 1 +0.5%*V, where V 1 is the first Bias voltage, and V is a half-wave voltage, where the half-wave voltage is a parameter of the MZ modulator.