MC-CDMA (multicarriercode division multiple access) is an important multiple access technique for mobile communications. In conventional MC-CDMA, construction of spreading sequences and multiuser detection are considered separately, which means that the transmitter and the receiver are not designed jointly. Inspired by LDPC (low density parity check) codes, the transceiver models of MC-CDMA based on graph theory were designed, and the low density Tanner graph was used to describe the relationship between spreading chips and data symbols. In addition, message passing algorithm, which was suitable for the Tanner graph, was utilized to perform iterative multiuser detection. Flooding and serial schedules for the message passing were deduced and analyzed. Simulation results show that the conventional MC-CDMA cannot perform well under the overloading conditions, while the proposed low density Tanner graph for MC-CDMA achieves satisfactory performance, which provides the useful reference for the design of next generation mobile networks.