The invention discloses a method of channel multiplexing in a relay-based cellular cell, including: at a mobile terminal accessing a network, judging whether the terminal itself is a single-hop user directly covered by a base station or a double-hop user covered by the relay by monitoring notification information from a base station and a relay station in the network, further judging which relay station's coverage the terminal itself belongs to if the terminal is the double-hop user, and feeding the information of the relay station to which the terminal itself belongs back to the base station via the relevant relay station; at the base station, allocating a channel to the current mobile terminal; and between the base station and the mobile terminal, then transmitting data via the relay station to which the relevant mobile terminal belongs, using the allocated channel. The invention also provides a mobile communication system and the relay using the above channel multiplexing method. The inventive method and the mobile communication system can effectively use the channel multiplexing gain brought by the space independence, thereby increasing the system throughput and the channel use ratio.