An apparatus for monitoring an optical performance parameter, comprising: a coherent receiving unit, configured to perform coherent synthesis on a received to-be-detected optical signal and a multi-wavelength local oscillation laser beam, and convert a coherent receiving signal formed by means of the coherent synthesis into an analog electrical signal; a data acquiring unit, configured to acquire the analog electrical signal output by the coherent receiving unit, and convert the analog electrical signal into a digital signal; a power spectrum generation unit, configured to process the digital signal output by the data acquiring unit, to generate a continuous full power spectrum of the to-be-detected optical signal; and an optical performance parameter monitoring unit, configured to monitor, according to the continuous full power spectrum generated by the power spectrum generation unit, an optical performance parameter of a transmission link carrying the to-be-detected optical signal, wherein the continuous full power spectrum indicates a continuous power spectrum of the to-be-detected optical signal in an entire to-be-detected frequency band; wherein the power spectrum generation unit comprises: a Fourier transform module, configured to perform Fourier transformation on the digital signal output by the data acquiring unit, to generate continuous power spectra, in multiple different frequency bands corresponding to the multi-wavelength local oscillation laser beam, of the to-be-detected optical signal; a spectrum splicing module, configured to generate a discrete full power spectrum of the to-be-detected optical signal according to the continuous power spectra in the multiple different frequency bands; and a spectrum generation module, configured to generate the continuous full power spectrum of the to-be-detected optical signal according to the discrete full power spectrum of the to-be-detected optical signal by using an interpolation algorithm. a coherent receiving unit, configured to perform coherent synthesis on a received to-be-detected optical signal and a multi-wavelength local oscillation laser beam, and convert a coherent receiving signal formed by means of the coherent synthesis into an analog electrical signal; a data acquiring unit, configured to acquire the analog electrical signal output by the coherent receiving unit, and convert the analog electrical signal into a digital signal; a power spectrum generation unit, configured to process the digital signal output by the data acquiring unit, to generate a continuous full power spectrum of the to-be-detected optical signal; and an optical performance parameter monitoring unit, configured to monitor, according to the continuous full power spectrum generated by the power spectrum generation unit, an optical performance parameter of a transmission link carrying the to-be-detected optical signal, wherein the continuous full power spectrum indicates a continuous power spectrum of the to-be-detected optical signal in an entire to-be-detected frequency band; wherein the power spectrum generation unit comprises: a Fourier transform module, configured to perform Fourier transformation on the digital signal output by the data acquiring unit, to generate continuous power spectra, in multiple different frequency bands corresponding to the multi-wavelength local oscillation laser beam, of the to-be-detected optical signal; a spectrum splicing module, configured to generate a discrete full power spectrum of the to-be-detected optical signal according to the continuous power spectra in the multiple different frequency bands; and a spectrum generation module, configured to generate the continuous full power spectrum of the to-be-detected optical signal according to the discrete full power spectrum of the to-be-detected optical signal by using an interpolation algorithm. a Fourier transform module, configured to perform Fourier transformation on the digital signal output by the data acquiring unit, to generate continuous power spectra, in multiple different frequency bands corresponding to the multi-wavelength local oscillation laser beam, of the to-be-detected optical signal; a spectrum splicing module, configured to generate a discrete full power spectrum of the to-be-detected optical signal according to the continuous power spectra in the multiple different frequency bands; and a spectrum generation module, configured to generate the continuous full power spectrum of the to-be-detected optical signal according to the discrete full power spectrum of the to-be-detected optical signal by using an interpolation algorithm.