The present invention discloses an apparatus. The apparatus includes: 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.