The present invention relates to the technical field of communications, and particularly, to an optical add/drop multiplexer, which is used for enabling the optical add/drop multiplexer to ensure that light in two directions is correctly processed. According to the optical add/drop multiplexer, a signal in one direction can be separated out by means of one microring resonant cavity and two optical circulators; meanwhile, a signal in the other direction can again enter an optical network by means of two microring resonant cavities and one optical circulator if the wavelength of the signal is the same as the resonant wavelengths of the microring resonant cavities, and the signal is not affected. In this way, optical signals in the two directions can be correctly processed, and there is no interference between the optical signals.