Embodiments of the present invention provide an optical add/drop multiplexer, including a plurality of tunable optical add/drop multiplexers T-OADMs. Each T-OADM includes a second wavelength control unit and two grating-assisted filters GAFs. The second wavelength control unit is connected to a second GAF. A drop port of a first GAF is connected to an input port of the second GAF. An add port of the first GAF is connected to an output port of the second GAF. An input port of the first GAF receives light waves of a plurality of wavelengths. The first GAF transmits a first light wave to the input port of the second GAF through the drop port of the first GAF. The second wavelength control unit changes a dropped spectrum of the second GAF based on first amplitude of wavelength shift, to obtain a first light wave response.