Embodiments of the present invention provide a method and an apparatus for transmitting and receiving a client signal, and relate to the field of communications technologies. The method includes: mapping the client signal into channels of a parallel transmission frame, where the parallel transmission frame includes at least two channels; adding an overhead for the channels of the parallel transmission frame after the mapping, to form transmission channels of the parallel transmission frame, where bit rates of the transmission channels of the parallel transmission frame are fixed; and modulating the transmission channels of the parallel transmission frame onto one or more optical carriers in a same optical fiber, and transmitting the optical carrier after the modulation.