Provided are methods, apparatuses and a system for monitoring a Reconfigurable Optical Add Drop Multiplexer (ROADM) optical network. The method includes: loading, in an optical signal at a sending end, a wavelength label frequency and attribute information of a channel used for transmitting the optical signal; sending the wavelength label frequency and/or the attribute information; receiving, at a monitoring end, the optical signal and acquiring, from the optical signal, the wavelength label frequency and/or the attribute information of the channel used for transmitting the optical signal; and monitoring the ROADM optical network according to the wavelength label frequency and/or the attribute information. The technical solution solves the technical problem in related art that the ROADM optical network cannot be effectively monitored, and achieves the effective monitoring of the ROADM optical network.