An optical signal detection method, comprising: receiving, by a frequency mixer, wavelength division multiplexing signals and a local oscillator signal, wherein a wavelength of the local oscillator signal and a wavelength of a target signal in the wavelength division multiplexing signals are the same; performing, by the frequency mixer, interference on the wavelength division multiplexing signals through the local oscillator signal to obtain a coherent signal formed by the local oscillator signal and the target signal; converting, by the frequency mixer, the coherent signal from an optical signal into an electric signal, and sending the converted coherent signal to a transimpedance amplifier for amplification to obtain a voltage signal, and then sending the voltage signal to a variable-gain amplifier, characterized in that, the signal detection method further comprises: obtaining power of the target signal according to a feedback voltage signal of an output end of the variable-gain amplifier, wherein the variable-gain amplifier is configured to amplify the voltage signal according to a feedback voltage of an output end of the variable-gain amplifier, and generate an output signal of constant power, the obtaining the power of the target signal according to the feedback voltage signal of the output end of the variable-gain amplifier comprises: according to voltage of the feedback voltage signal of the output end of the variable-gain amplifier, searching a preset mapping function, mapping curve or mapping table to obtain the power of the target signal. receiving, by a frequency mixer, wavelength division multiplexing signals and a local oscillator signal, wherein a wavelength of the local oscillator signal and a wavelength of a target signal in the wavelength division multiplexing signals are the same; performing, by the frequency mixer, interference on the wavelength division multiplexing signals through the local oscillator signal to obtain a coherent signal formed by the local oscillator signal and the target signal; converting, by the frequency mixer, the coherent signal from an optical signal into an electric signal, and sending the converted coherent signal to a transimpedance amplifier for amplification to obtain a voltage signal, and then sending the voltage signal to a variable-gain amplifier, characterized in that, the signal detection method further comprises: obtaining power of the target signal according to a feedback voltage signal of an output end of the variable-gain amplifier, wherein the variable-gain amplifier is configured to amplify the voltage signal according to a feedback voltage of an output end of the variable-gain amplifier, and generate an output signal of constant power, the obtaining the power of the target signal according to the feedback voltage signal of the output end of the variable-gain amplifier comprises: according to voltage of the feedback voltage signal of the output end of the variable-gain amplifier, searching a preset mapping function, mapping curve or mapping table to obtain the power of the target signal. obtaining power of the target signal according to a feedback voltage signal of an output end of the variable-gain amplifier, wherein the variable-gain amplifier is configured to amplify the voltage signal according to a feedback voltage of an output end of the variable-gain amplifier, and generate an output signal of constant power, the obtaining the power of the target signal according to the feedback voltage signal of the output end of the variable-gain amplifier comprises: according to voltage of the feedback voltage signal of the output end of the variable-gain amplifier, searching a preset mapping function, mapping curve or mapping table to obtain the power of the target signal. according to voltage of the feedback voltage signal of the output end of the variable-gain amplifier, searching a preset mapping function, mapping curve or mapping table to obtain the power of the target signal.