Embodiments of the present invention provide a method and an apparatus for transmitting and receiving a client signal in an optical transport network. In the transmission method, a received client signal is mapped into a variable-rate container OTU-N, wherein a rate of the OTU-N is N times as high as a preset reference rate; and then, the variable-rate container OTU-N is split into N optical sub-channel transport units OTUsubs by column, where a rate of each OTUsub equals to the reference rate; next, the N optical sub-channel transport units OTUsubs are modulated onto one or more optical carriers; at last, the one or more optical carriers is transmitted through a fiber.