The present invention discloses an optical power monitoring method and apparatus. The present invention includes: measuring broadened spectrums of optical signals of monitored channels after performing filtering processing on the optical signals, to obtain a measured broadened spectrum of the optical signals of the monitored channels; constructing a plurality of optical signal power combinations; performing calculation for each optical signal power combination according to a transfer function that indicates the filtering processing, to obtain its corresponding theoretical broadened spectrum of the optical signals of the monitored channels; comparing a plurality of theoretical broadened spectrums with the measured broadened spectrum to find a theoretical broadened spectrum that is closest to the measured broadened spectrum; and determining each hypothetical optical power in an optical signal power combination corresponding to the theoretical broadened spectrum as an actual optical power of an optical signal of a corresponding monitored channel.